Swift编程指南：从基础到高级

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"Swift用户指南提供了关于Swift编程语言的详细信息，包括语言基础、数组与并行执行、关联数组、执行顺序、复合过程、类型系统、数据模型、映射器的深入技术细节以及控制结构等。此外，还涵盖了变量、赋值语句、过程、控制构造（如for-each、if、switch、iterate）、运算符、全局常量和导入模块等内容。指南还专门介绍了不同类型的映射器，如单文件映射器、简单映射器、并发映射器、文件系统映射器、固定数组映射器和数组映射器，这些映射器是Swift在处理大规模数据时的重要工具。" Swift是一种由Apple开发的开源编程语言，主要用于构建iOS、macOS、watchOS和tvOS的应用程序。在本用户指南中，我们深入探讨了Swift语言的核心概念： 1. **语言基础**：Swift的基础包括语法、变量、常量、函数和控制流程，这些都是编写任何程序的基石。 2. **数组和并行执行**：Swift支持数组操作，并且可以利用多核处理器进行并行计算，提高性能。 3. **关联数组**：这种数据结构允许您使用键值对存储数据，键可以用来快速访问对应的值。 4. **执行顺序**：了解代码的执行顺序对于理解程序逻辑至关重要，Swift支持顺序执行、分支和循环。 5. **复合过程**：通过组合简单的操作，可以创建更复杂的任务，这在编写大型程序时非常有用。 6. **类型系统**：Swift具有强类型特性，支持多种内置类型，如整型、浮点型、布尔型，还有可选类型用于处理可能的null值。 7. **数据模型**：定义和管理数据的结构，包括结构体、枚举等。 8. **映射器（Mappers）**：这是Swift中处理大量数据的关键部分，不同的映射器适应不同的数据处理场景，例如并行处理、文件系统交互等。 9. **控制构造**：Swift的控制流语句（如for-each、if、switch、iterate）让开发者能够根据条件改变程序执行路径。 10. **运算符**：Swift支持标准算术、比较和逻辑运算符，还可以自定义运算符。 11. **全局常量**：在程序全局范围内定义的不可变值。 12. **导入模块**：Swift通过导入模块来组织代码，使得大型项目易于管理和重用。本指南的目标是帮助开发者掌握Swift语言，无论是初学者还是经验丰富的程序员，都能从中受益，提升Swift编程技能。通过学习这些知识点，开发者将能够有效地构建高效、安全的Swift应用程序。

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Statements which deal with the array as a whole will often wait for the array to be closed before executing (thus, a closed array

is the equivalent of a non-array type being assigned). However, a foreach statement will apply its body to elements of an array as

they become known. It will not wait until the array is closed.

Consider this script:

file a[];

file b[];

foreach v,i in a {

b[i] = p(v);

}

a[0] = r();

a[1] = s();

Initially, the foreach statement will have nothing to execute, as the array a has not been assigned any values. The procedures r

and s will execute. As soon as either of them is ﬁnished, the corresponding invocation of procedure p will occur. After both r and

s have completed, the array a will be closed since no other statements in the script make an assignment to a.

2.5 Compound procedures

As with many other programming languages, procedures consisting of Swift script can be deﬁned. These differ from the pre-

viously mentioned procedures declared with the app keyword, as they invoke other Swift procedures rather than a component

program.

(file output) process (file input) {

file intermediate;

intermediate = first(input);

output = second(intermediate);

}

file x <"x.txt">;

file y <"y.txt">;

y = process(x);

This will invoke two procedures, with an intermediate data ﬁle named anonymously connecting the ﬁrst and second procedures.

Ordering of execution is generally determined by execution of app procedures, not by any containing compound procedures. In

this code block:

(file a, file b) A() {

a = A1();

b = A2();

}

file x, y, s, t;

(x,y) = A();

s = S(x);

t = S(y);

then a valid execution order is: A1 S(x) A2 S(y). The compound procedure A does not have to have fully completed for its return

values to be used by subsequent statements.

2.6 More about types

Each variable and procedure parameter in Swift script is strongly typed. Types are used to structure data, to aid in debugging and

checking program correctness and to inﬂuence how Swift interacts with data.

The image type declared in previous examples is a marker type. Marker types indicate that data for a variable is stored in a single

ﬁle with no further structure exposed at the Swift script level.

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type contains

int integers

string strings of text

ﬂoat ﬂoating point numbers, that behave the same as Java

doubles

boolean true/false

Complex types may be deﬁned using the type keyword:

type headerfile;

type voxelfile;

type volume {

headerfile h;

voxelfile v;

}

Members of a complex type can be accessed using the . operator:

volume brain;

o = p(brain.h);

Sometimes data may be stored in a form that does not ﬁt with Swift’s ﬁle-and-site model; for example, data might be stored in

an RDBMS on some database server. In that case, a variable can be declared to have external type. This indicates that Swift

should use the variable to determine execution dependency, but should not attempt other data management; for example, it will

not perform any form of data stage-in or stage-out it will not manage local data caches on sites; and it will not enforce component

program atomicity on data output. This can add substantial responsibility to component programs, in exchange for allowing

arbitrary data storage and access methods to be plugged in to scripts.

type file;

app (external o) populateDatabase() {

populationProgram;

}

app (file o) analyseDatabase(external i) {

analysisProgram @o;

}

external database;

file result <"results.txt">;

database = populateDatabase();

result = analyseDatabase(database);

Some external database is represented by the database variable. The populateDatabase procedure populates the database with

some data, and the analyseDatabase procedure performs some subsequent analysis on that database. The declaration of database

contains no mapping; and the procedures which use database do not reference them in any way; the description of database is

entirely outside of the script. The single assignment and execution ordering rules will still apply though; populateDatabase will

always be run before analyseDatabase.

2.7 Data model

Data processed by Swift is strongly typed. It may be take the form of values in memory or as out-of-core ﬁles on disk. Language

constructs called mappers specify how each piece of data is stored.

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