The way to go

go程序设计语言 Contents Preface................................................................................................................................. xix PART 1—WHY LEARN GO—GETTING STARTED Chapter 1—Origins, Context and Popularity of Go...............................................................1 1.1 Origins and evolution................................................................................................1 1.2 Main characteristics, context and reasons for developing a new language....................4 1.2.1 Languages that influenced Go.........................................................................4 1.2.2 Why a new language?......................................................................................5 1.2.3 Targets of the language....................................................................................5 1.2.4 Guiding design principles...............................................................................7 1.2.5 Characteristics of the language........................................................................7 1.2.6 Uses of the language........................................................................................8 1.2.7 Missing features?.............................................................................................9 1.2.8 Programming in Go......................................................................................10 1.2.9 Summary......................................................................................................10 Chapter 2—Installation and Runtime Environment............................................................11 2.1 Platforms and architectures.....................................................................................11 (1) The gc Go-compilers:..................................................................................11 (2) The gccgo-compiler:....................................................................................13 (3) File extensions and packages:.......................................................................14 2.2 Go Environment variables........................................................................................14 2.3 Installing Go on a Linux system...............................................................................16 2.4 Installing Go on an OS X system.............................................................................21 2.5 Installing Go on a Windows system.........................................................................21 2.6 What is installed on your machine? .........................................................................26 2.7 The Go runtime.......................................................................................................27 2.8 A Go interpreter ......................................................................................................27 Chapter 3—Editors, IDE’s and Other tools.........................................................................28 3.1 Basic requirements for a decent Go development environment.................................28 3.2 Editors and Integrated Development Environments.................................................29 3.2.1. Golang LiteIDE ..........................................................................................32 3.2.2. GoClipse......................................................................................................33 3.3 Debuggers................................................................................................................34 3.4 Building and running go-programs with command- and Makefiles..........................35 3.5 Formatting code: go fmt or gofmt............................................................................39 3.6 Documenting code: go doc or godoc........................................................................40 3.7 Other tools...............................................................................................................41 3.8 Go’s performance.....................................................................................................41 3.9 Interaction with other languages...............................................................................43 3.9.1. Interacting with C .......................................................................................43 3.9.2. Interacting with C++....................................................................................45 PART 2—CORE CONSTRUCTS AND TECHNIQUES OF THE LANGUAGE Chapter 4—Basic constructs and elementary data types.......................................................49 4.1. Filenames—Keywords—Identifiers..........................................................................49 4.2. Basic structure and components of a Go-program...................................................50 4.2.1 Packages, import and visibility......................................................................51 4.2.3 Comments....................................................................................................56 4.2.4 Types............................................................................................................57 4.2.5 General structure of a Go-program...............................................................58 4.2.6 Conversions..................................................................................................60 4.2.7 About naming things in Go..........................................................................60 4.3. Constants................................................................................................................60 4.4. Variables..................................................................................................................63 4.4.1 Introduction.................................................................................................63 4.4.2 Value types and reference types.....................................................................66 4.4.3 Printing........................................................................................................68 4.4.4 Short form with the := assignment operator..................................................69 4.4.5 Init-functions................................................................................................70 4.5. Elementary types and operators...............................................................................73 4.5.1. Boolean type bool........................................................................................73 4.5.2. Numerical types...........................................................................................75 4.5.2.1 ints and floats.............................................................................................75 4.5.2.2 Complex numbers.....................................................................................79 4.5.2.3 Bit operators..............................................................................................79 4.5.2.4 Logical operators........................................................................................81 4.5.2.5 Arithmetic operators.................................................................................82 4.5.2.6 Random numbers......................................................................................82 4.5.3. Operators and precedence............................................................................84 4.5.4. Aliasing types...............................................................................................84 4.5.5. Character type.............................................................................................85 4.6. Strings.....................................................................................................................86 4.7. The strings and strconv package..............................................................................88 4.7.1—Prefixes and suffixes:...................................................................................88 4.7.2—Testing whether a string contains a substring:.............................................89 4.7.3—Indicating at which position (index) a substring or character occurs in a string:...................................................................................................89 4.7.4—Replacing a substring:................................................................................90 4.7.5—Counting occurrences of a substring:..........................................................90 4.7.6—Repeating a string:.....................................................................................90 4.7.7—Changing the case of a string:....................................................................91 4.7.8—Trimming a string:.....................................................................................92 4.7.9—Splitting a string:........................................................................................92 4.7.10—Joining over a slice:..................................................................................92 4.7.11—Reading from a string:..............................................................................93 4.8. Times and dates.......................................................................................................95 4.9. Pointers...................................................................................................................96 Chapter 5—Control structures...........................................................................................101 5.1—The if else construct............................................................................................101 5.2—Testing for errors on functions with multiple return values..................................106 5.3—The switch keyword............................................................................................110 5.4—The for construct................................................................................................114 5.4.1 Counter-controlled iteration.......................................................................114 Character on position 2 is:...........................................................................................116 5.4.2 Condition-controlled iteration ...................................................................117 5.4.3 Infinite loops .............................................................................................118 5.4.4 The for range construct...............................................................................119 5.5—Break / continue..................................................................................................121 5.6—Use of labels with break and continue—goto.......................................................123 Chapter 6—Functions.......................................................................................................126 6.1 Introduction...........................................................................................................126 6.2 Parameters and return values..................................................................................129 6.2.1 Call by value / Call by reference..................................................................129 6.2.2 Named return variables...............................................................................131 6.2.3 Blank identifier...........................................................................................133 6.2.4 Changing an outside variable......................................................................134 6.3 Passing a variable number of parameters.................................................................135 6.4 Defer and tracing...................................................................................................137 6.5 Built-in functions...................................................................................................142 6.6 Recursive functions................................................................................................143 6.8 Closures (function literals).....................................................................................147 6.9 Applying closures: a function returning another function ......................................150 6.10 Debugging with closures......................................................................................153 6.11 Timing a function ...............................................................................................154 6.12 Using memoization for performance....................................................................154 Chapter 7—Arrays and Slices.............................................................................................157 7.1 Declaration and initialization.................................................................................157 7.1.1 Concept......................................................................................................157 7.1.2 Array literals................................................................................................161 7.1.3 Multidimensional arrays..............................................................................162 7.1.4 Passing an array to a function......................................................................163 7.2 Slices......................................................................................................................164 7.2.1 Concept......................................................................................................164 7.2.2 Passing a slice to a function.........................................................................168 7.2.3 Creating a slice with make()........................................................................168 7.2.4 Difference between new() and make().........................................................170 7.2.5 Multidimensional slices...............................................................................171 7.2.6 The bytes package.......................................................................................171 7.3 For range construct................................................................................................172 7.4 Reslicing.................................................................................................................175 7.5 Copying and appending slices................................................................................176 7.6 Applying strings, arrays and slices...........................................................................178 7.6.1 Making a slice of bytes from a string...........................................................178 7.6.2 Making a substring of a string.....................................................................179 7.6.3 Memory representation of a string and a slice..............................................179 7.6.4 Changing a character in a string..................................................................180 7.6.5 Comparison function for byte arrays...........................................................180 7.6.6 Searching and sorting slices and arrays.......................................................181 7.6.7 Simulating operations with append.............................................................182 7.6.8 Slices and garbage collection.......................................................................182 Chapter 8—Maps..............................................................................................................185 8.1 Declaration, initialization and make.......................................................................185 8.1.1 Concept......................................................................................................185 8.1.2 Map capacity..............................................................................................188 8.1.3 Slices as map values.....................................................................................188 8.2 Testing if a key-value item exists in a map—Deleting an element...........................188 8.3 The for range construct..........................................................................................190 8.4 A slice of maps......................................................................................................191 8.5 Sorting a map.........................................................................................................192 8.6 Inverting a map......................................................................................................194 Chapter 9—Packages.........................................................................................................196 A The standard library..................................................................................................196 9.1 Overview of the standard library.............................................................................196 9.2 The regexp package................................................................................................199 9.3 Locking and the sync package................................................................................200 9.4 Accurate computations and the big package...........................................................202 B Custom and external packages: use, build, test, document, install.............................203 9.5 Custom packages and visibility...............................................................................203 9.6 Using godoc for your custom packages...................................................................208 9.7 Using go install for installing custom packages.......................................................210 9.8 Custom packages: map structure, go install and go test..........................................212 9.8.1 Map-structure for custom packages.............................................................212 9.8.2 Locally installing the package......................................................................215 9.8.3 OS dependent code.....................................................................................216 9.9 Using git for distribution and installation...............................................................216 9.9.1 Installing to github.....................................................................................216 9.9.2 Installing from github.................................................................................217 9.10 Go external packages and projects. ......................................................................218 9.11 Using an external library in a Go program............................................................219 Chapter 10—Structs and Methods.....................................................................................224 10.1 Definition of a struct............................................................................................224 10.2 Creating a struct variable with a Factory method..................................................232 10.2.1 A factory for structs..................................................................................232 10.2.2 new() and make() revisited for maps and structs:.......................................234 10.3 Custom package using structs...............................................................................235 10.4 Structs with tags...................................................................................................236 10.5 Anonymous fields and embedded structs..............................................................237 10.5.1 Definition.................................................................................................237 10.5.2 Embedded structs.....................................................................................238 10.5.3 Conflicting names.....................................................................................239 10.6 Methods...............................................................................................................240 10.6.1 What is a method?....................................................................................240 10.6.2 Difference between a function and a method............................................244 10.6.3 Pointer or value as receiver........................................................................245 10.6.4 Methods and not-exported fields..............................................................247 10.6.5 Methods on embedded types and inheritance............................................248 10.6.6 How to embed functionality in a type.......................................................251 10.6.7 Multiple inheritance..................................................................................253 10.6.8 Universal methods and method naming....................................................256 10.6.9 Comparison between Go types and methods and other object-oriented languages...........................................................................256 10.7 The String()-method and format specifiers for a type...........................................258 10.8 Garbage collection and SetFinalizer......................................................................261 Chapter 11—Interfaces and reflection................................................................................263 11.1 What is an interface?............................................................................................263 11.2 Interface embedding interface(s)...........................................................................270 11.3 How to detect and convert the type of an interface variable: type assertions.........270 11.4 The type switch....................................................................................................273 11.5 Testing if a value implements an interface.............................................................274 11.6 Using method sets with interfaces.........................................................................275 11.7 1st example: sorting with the Sorter interface........................................................277 11.8 2nd example: Reading and Writing......................................................................282 11.9 Empty Interface...................................................................................................284 11.9.1 Concept....................................................................................................284 11.9.2 Constructing an array of a general type or with variables of different types............................................................................................286 11.9.3 Copying a data-slice in a slice of interface{}...............................................287 11.9.4 Node structures of general or different types.............................................288 11.9.5 Interface to interface.................................................................................289 11.10 The reflect package.............................................................................................290 11.10.1 Methods and types in reflect...................................................................290 11.10.2 Modifying (setting) a value through reflection........................................293 11.10.3 Reflection on structs...............................................................................294 11.11 Printf and reflection...........................................................................................296 11.12 Interfaces and dynamic typing............................................................................298 11.12.1 Dynamic typing in Go............................................................................298 11.12.2 Dynamic method invocation...................................................................300 11.12.3 Extraction of an interface........................................................................301 11.12.4 Explicitly indicating that a type implements an interface........................303 11.12.5 Empty interface and function overloading..............................................304 11.12.6 Inheritance of interfaces..........................................................................304 11.13 Summary: the object-orientedness of Go............................................................306 11.14 Structs, collections and higher order functions...................................................306 PART 3—ADVANCED GO Chapter 12—Reading and writing.....................................................................................313 12.1 Reading input from the user.................................................................................313 12.2 Reading from and writing to a file........................................................................317 12.2.1 Reading from a file....................................................................................317 12.2.2 The package compress: reading from a zipped file.....................................321 12.2.3 Writing to a file.........................................................................................322 12.3 Copying files........................................................................................................324 12.4 Reading arguments from the command-line.........................................................325 12.4.1 With the os-package..................................................................................325 12.4.2 With the flag-package...............................................................................326 12.5 Reading files with a buffer....................................................................................328 12.6 Reading and writing files with slices.....................................................................330 12.7 Using defer to close a file.....................................................................................332 12.8 A practical example of the use of interfaces: fmt.Fprintf......................................332 12.9 The json dataformat.............................................................................................334 12.10 The xml dataformat............................................................................................340 12.11 Datatransport through gob.................................................................................342 12.12 Cryptography with go........................................................................................345 Chapter 13—Error-handling and Testing...........................................................................348 13.1 Error-handling.....................................................................................................349 13.1.1 Defining errors..........................................................................................349 13.1.2 Making an error-object with fmt..............................................................353 13.2 Run-time exceptions and panic............................................................................353 13.4 Error-handling and panicking in a custom package..............................................357 13.5 An error-handling scheme with closures...............................................................360 13.6 Starting an external command or program...........................................................363 13.7 Testing and benchmarking in Go.........................................................................364 13.8 Testing: a concrete example..................................................................................367 13.9 Using table-driven tests........................................................................................369 13.10 Investigating performance: tuning and profiling Go programs............................371 13.10.1 Time and memory consumption.............................................................371 13.10.2 Tuning with go test.................................................................................371 13.10.3 Tuning with pprof...................................................................................371 Chapter 14—Goroutines and Channels.............................................................................375 14.1 Concurrency, parallelism and goroutines..............................................................375 14.1.1 What are goroutines?................................................................................375 14.1.2 The difference between concurrency and parallelism.................................377 14.1.3 Using GOMAXPROCS............................................................................378 14.1.4 How to specify the number of cores to be used on the command-line?.....379 14.1.5 Goroutines and coroutines........................................................................381 14.2 Channels for communication between goroutines................................................381 14.2.1 Concept....................................................................................................381 14.2.2 Communication operator <-.....................................................................383 14.2.3 Blocking of channels.................................................................................385 14.2.4 Goroutines synchronize through the exchange of data on one (or more) channel(s)........................................................................................387 14.2.5 Asynchronous channels—making a channel with a buffer.........................387 14.2.6 Goroutine using a channel for outputting result(s)....................................388 14.2.7 Semaphore pattern....................................................................................389 14.2.8 Implementing a parallel for-loop...............................................................391 14.2.9 Implementing a semaphore using a buffered channel................................391 14.2.10 For—range applied to channels...............................................................394 14.2.11 Channel directionality............................................................................396 14.3 Synchronization of goroutines: closing a channel—testing for blocked channels..400 14.4 Switching between goroutines with select.............................................................403 14.5 Channels, Timeouts and Tickers...........................................................................408 14.6 Using recover with goroutines..............................................................................412 14.7 Comparing the old and the new model: Tasks and Worker processes....................413 14.8 Implementing a lazy generator..............................................................................416 14.9 Implementing Futures..........................................................................................420 14.10 Multiplexing......................................................................................................421 14.10.1 A typical client-server pattern..................................................................421 14.10.2 Teardown: shutdown the server by signaling a channel............................424 14.11 Limiting the number of requests processed concurrently....................................427 14.12 Chaining goroutines...........................................................................................428 14.13 Parallelizing a computation over a number of cores............................................429 14.14 Parallelizing a computation over a large amount of data.....................................430 14.15 The leaky bucket algorithm................................................................................431 14.16 Benchmarking goroutines...................................................................................433 14.17 Concurrent acces to objects by using a channel..................................................434 Chapter 15—Networking, templating and web-applications..............................................436 15.1 A tcp-server .........................................................................................................436 15.2 A simple webserver...............................................................................................445 15.3 Polling websites and reading in a web page...........................................................448 15.4 Writing a simple web application.........................................................................452 15.5 Making a web application robust..........................................................................454 15.6 Writing a web application with templates.............................................................456 15.7 Exploring the template package............................................................................461 15.7.1. Field substitution: {{.FieldName}}............................................................462 15.7.2. Validation of the templates.......................................................................463 15.7.3 If-else........................................................................................................464 15.7.4 Dot and with-end.....................................................................................465 15.7.5 Template variables $..................................................................................466 15.7.6 Range-end.................................................................................................467 15.7.7 Predefined template functions...................................................................467 15.8 An elaborated webserver with different functions.................................................468 (works only on Unix because calls /bin/date)........................................................474 15.9 Remote procedure calls with rpc...........................................................................474 15.10 Channels over a network with netchan...............................................................477 15.11 Communication with websocket........................................................................478 15.12 Sending mails with smtp....................................................................................480 PART 4—APPLYING GO Chapter 16—Common Go Pitfalls or Mistakes..................................................................485 16.1 Hiding (shadowing) a variable by misusing short declaration...............................486 16.2 Misusing strings...................................................................................................486 16.3 Using defer for closing a file in the wrong scope...................................................487 16.4 Confusing new() and make()................................................................................488 16.5 No need to pass a pointer to a slice to a function..................................................488 16.6 Using pointers to interface types...........................................................................488 16.7 Misusing pointers with value types.......................................................................489 16.8 Misusing goroutines and channels........................................................................489 16.9 Using closures with goroutines.............................................................................490 16.10 Bad error handling.............................................................................................491 16.10.1 Don’t use booleans:.................................................................................491 16.10.2 Don’t clutter your code with error-checking:...........................................492 Chapter 17—Go Language Patterns...................................................................................494 17.1 The comma, ok pattern........................................................................................494 17.2 The defer pattern..................................................................................................495 17.3 The visibility pattern............................................................................................497 17.4 The operator pattern and interface.......................................................................497 17.4.1 Implement the operators as functions.......................................................497 17.4.2 Implement the operators as methods.........................................................498 17.4.3 Using an interface.....................................................................................499 Chapter 18—Useful Code Snippets—Performance Advice.................................................500 18.1 Strings..................................................................................................................500 18.2 Arrays and slices...................................................................................................501 18.3 Maps....................................................................................................................502 18.4 Structs..................................................................................................................502 18.5 Interfaces..............................................................................................................503 18.6 Functions.............................................................................................................503 18.7 Files......................................................................................................................504 18.8 Goroutines and channels......................................................................................505 18.9 Networking and web applications.........................................................................507 18.9.1. Templating:......................................................................................................507 18.10 General..............................................................................................................508 18.11 Performance best practices and advice................................................................508 Chapter 19—Building a complete application....................................................................509 19.1 Introduction.........................................................................................................509 19.2 Introducing Project UrlShortener.........................................................................509 19.3 Data structure......................................................................................................510 19.4 Our user interface: a web server frontend.............................................................515 19.5 Persistent storage: gob..........................................................................................519 19.6 Using goroutines for performance........................................................................524 19.7 Using json for storage...........................................................................................527 19.8 Multiprocessing on many machines......................................................................528 19.9 Using a ProxyStore...............................................................................................532 19.10 Summary and enhancements..............................................................................536 Chapter 20—Go in Google App Engine............................................................................538 20.1 What is Google App Engine ?...............................................................................538 20.2 Go in the cloud ...................................................................................................540 20.3 Installation of the Go App Engine SDK: the development environment for Go...540 20.3.1. Installation...............................................................................................540 20.3.2. Checking and testing...............................................................................542 20.4 Building your own Hello world app ....................................................................543 20.4.1 Map structure—Creating a simple http-handler........................................543 20.4.2 Creating the configuration file app.yaml...................................................544 20.4.3 Iterative development................................................................................548 20.4.4. Integrating with the GoClipse IDE..........................................................548 20.5 Using the Users service and exploring its API.......................................................549 20.6 Handling forms....................................................................................................551 20.7 Using the datastore...............................................................................................552 20.8 Uploading to the cloud.......................................................................................556 Chapter 21—Real World Uses of Go.................................................................................559 21.1 Heroku—a highly available consistent data store in Go. ......................................559 21.2 MROffice—a VOIP system for call centers in Go................................................561 21.3 Atlassian—a virtual machine cluster management system.....................................562 21.4 Camlistore—a content addressable storage system................................................563 21.5 Other usages of the Go language..........................................................................563 APPENDICES...................................................................................................................567 (A) CODE REFERENCE...........................................................................................567 (B)CUTE GO QUOTES.............................................................................................571 GO QUOTES: TRUE BUT NOT SO CUTE....................................................572 (C) LIST OF CODE EXAMPLES (Listings)...............................................................572 (E) References in the text to Go—packages..................................................................583 (F) References in the text to Go—tools........................................................................586 (G) Answers to Questions............................................................................................586 (H) ANSWERS TO EXERCISES................................................................................590 (I) BIBLIOGRAPHY (Resources and References)........................................................593 Index..............................................................................................................................597 List of Illustrations Chapter 1—Origins, Context and Popularity of Go...............................................................1 Fig 1.1: The designers of Go: Griesemer, Thompson and Pike..........................................1 Fig 1.2: The logo’s of Go..................................................................................................3 Fig 1.3: Influences on Go.................................................................................................5 Chapter 3—Editors, IDE’s and Other tools.........................................................................28 Fig 3.1: LiteIDE and its AST-view..................................................................................33 Fig 3.2: GoClipse and its outline code-view...................................................................34 Chapter 4—Basic constructs and elementary data types.......................................................49 Fig 4.1: Value type..........................................................................................................67 Fig 4.2: Assignment of value types..................................................................................67 Fig 4.3: Reference types and assignment.........................................................................67 Fig 4.4: Pointers and memory usage...............................................................................98 Fig 4.5: Pointers and memory usage, 2...........................................................................99 Chapter 7—Arrays and Slices.............................................................................................157 Fig 7.1: Array in memory.............................................................................................158 Fig 7.2: Slice in memory..............................................................................................166 Chapter 9—Packages.........................................................................................................196 Fig 9.1: Package documentation with godoc.................................................................210 Chapter 10—Structs and Methods.....................................................................................224 Fig 10.1: Memory layout of a struct.............................................................................227 Fig 10.2: Memory layout of a struct of structs..............................................................229 Fig. 10.3: Linked list as recursive struct........................................................................230 Fig 10.4: Binary tree as recursive struct.........................................................................230 Chapter 11—Interfaces and reflection................................................................................263 Fig 11.1: Interface value in memory.............................................................................264 Chapter 14—Goroutines and Channels.............................................................................375 Fig 14.1: Channels and goroutines...............................................................................382 Fig 14.2: The sieve prime-algorithm.............................................................................397 Chapter 15—Networking, templating and web-applications..............................................436 Fig 15.1—Screen of exercise 15.6.................................................................................454 Chapter 19—Building a complete application....................................................................509 Fig 19.1: Handler functions in goto.............................................................................515 Fig 19.2: The Add handler...........................................................................................518 Fig 19.3: The response of the Add handler...................................................................519 Fig 19.4: The response of the Redirect handler.............................................................519 Fig 19.5: Distributing the work load over master- and slave computers........................529 Chapter 20—Go in Google App Engine............................................................................538 Fig 20.1: The Application Control Panel......................................................................558