Lua 5.0编程参考手册

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"Lua 5.0 的参考手册是一个详细的技术文档，旨在为开发者提供关于 Lua 5.0 版本的全面指南。这个手册由 Tecgraf, PUC-Rio 创建并版权保护，允许自由复制、修改和分发，但需保留原始的版权信息。手册内容涵盖 Lua 语言的核心特性、语法、库函数以及编程接口等各个方面，是学习和使用 Lua 5.0 的重要参考资料。" Lua 是一种轻量级的脚本语言，设计目标是简洁、灵活和高效。在 Lua 5.0 版本中，主要知识点包括： 1. **语法基础**：Lua 语言具有简单的语法结构，支持变量（全局和局部）、数据类型（如数字、字符串、布尔值、表、函数、用户数据和 nil）以及控制结构（如条件语句、循环语句）。其中，表作为核心数据结构，可以用于实现数组、哈希、对象等。 2. **函数与作用域**：Lua 支持函数作为一等公民，可以作为参数传递，也可以作为返回值。局部变量的作用域限制在块级，这使得代码更易理解和管理。 3. **元表与元方法**：Lua 的表可以通过元表实现动态行为，元表中可以定义元方法，如索引操作和赋值操作的特殊处理。 4. **垃圾收集机制**：Lua 自带了自动垃圾收集机制，负责回收不再使用的内存，保证程序的内存效率。 5. **C 库接口**：Lua 通过 C API 提供与 C 语言的接口，使得 Lua 脚本可以调用 C 函数，或者将 C 代码嵌入到 Lua 程序中，扩展其功能。 6. **模块系统**：Lua 5.0 引入了模块系统，方便组织和管理代码，实现代码的封装和重用。 7. **错误处理**：Lua 通过异常处理机制来处理运行时错误，使用 `error` 函数抛出错误，并可以使用 `pcall` 或 `xpcall` 来捕获和处理错误。 8. **热更新**：Lua 代码可以在运行时加载和修改，这使得 Lua 成为游戏开发和其他需要动态调整逻辑的场景的理想选择。 9. **字符串处理**：Lua 的字符串是不可变的，提供了丰富的字符串操作函数，如拼接、查找、替换等。 10. **面向对象编程**：虽然 Lua 本身没有内置的类和继承概念，但通过元表和表可以实现类似面向对象的编程模式。 Lua 5.0 手册详细解释了这些概念，并通过实例展示了如何在实践中应用。无论是初学者还是经验丰富的开发者，都可以从中获取所需的信息，提升对 Lua 语言的理解和使用能力。

exchanges the values of x and y.

The m eaning of assignments to global variables and table ﬁelds can be changed via metatables.

An assignment to an indexed variable t[i] = val is equivalent to settable_event(t,i,val).

(See §2.8 for a complete description of the settable_event function. This function is not deﬁned

or callable in Lua. We use it here only for explanatory purposes.)

An assignment to a global variable x = val is equivalent to the assignment _env.x = val,

which in turn is equivalent to

settable_event(_env, "x", val)

where _env is the environment of the running function. (The _env variable is not deﬁned in Lua.

We use it here only for explanatory purposes.)

2.4.4 Control Structures

The control structures if, while, and repeat have the usual meaning and familiar s yntax:

stat → while exp do block end

stat → repeat block until exp

stat → if exp then block { elseif exp then block } [ else block ] end

Lua also has a for statement, in two ﬂavors (see §2.4.5).

The condition expression exp of a control structure may return any value. Both false and nil

are considered false. All values diﬀerent from nil and false are considered true (in particular, the

number 0 and the empty string are also true).

The return statement is used to return values from a function or from a chunk. Functions and

chunks may return more than one value, so the syntax for the return statement is

stat → return [ explist1 ]

The break statement can be used to terminate the execution of a while, repeat, or for loop,

skipping to the next statement after the loop:

stat → break

A break ends the innermost enclosing lo op.

For syntactic reasons, return and break statements can only be written as the last statement of

a block. If it is really necessary to return or break in the middle of a block, then an explicit inner

block can be used, as in the idioms ‘do return end’ and ‘do break end’, because now return

and break are the last statements in their (inner) blocks. In practice, those idioms are only used

during debugging.

2.4.5 For Statement

The for statement has two forms: one numeric and one generic.

The numeric for loop repeats a block of code while a control variable runs through an arithmetic

progression. It has the following syntax:

stat → for Name ‘=’ exp ‘,’ exp [ ‘,’ exp ] do block end

The block is repeated for name starting at the value of the ﬁrst exp, until it passes the second exp

by steps of the third exp. More precisely, a for statement like

for var = e1, e2, e3 do block end

• The behavior is undeﬁned if you assign to var_1 inside the block.

• You can use break to exit a for loop.

• The loop variables var_i are local to the statement; you cannot use their values after the for

ends. If you need these values, then assign them to other variables before breaking or exiting

the loop.

2.4.6 Function Calls as Statements

To allow possible side-eﬀects, function calls can be executed as statements:

stat → functioncall

In this case, all returned values are thrown away. Function calls are explained in §2.5.7.

2.4.7 Local Declarations

Local variables may be declared anywhere inside a blo ck. The declaration may include an initial

assignment:

stat → local namelist [ ‘=’ explist1 ]

namelist → Name { ‘,’ Name }

If present, an initial assignment has the same semantics of a multiple assignment (see §2.4.3).

Otherwise, all variables are initialized with nil.

A chunk is also a block (see §2.4.1), so local variables can be declared in a chunk outside any

explicit block. Such local variables die when the chunk ends.

The visibility rules for local variables are explained in §2.6.

2.5 Expressions

The basic expressions in Lua are the following:

exp → preﬁxexp

exp → nil | false | true

exp → Number

exp → Literal

exp → function

exp → tableconstructor

preﬁxexp → var | functioncall | ‘(’ exp ‘)’

Numbers and literal strings are explained in §2.1; variables are explained in §2.3; function

deﬁnitions are explained in §2.5.8; function calls are explained in §2.5.7; table constructors are

explained in §2.5.6.

An expression enclosed in parentheses always results in only one value. Thus, (f(x,y,z)) is

always a single value, e ven if f returns several values. (The value of (f(x,y,z)) is the ﬁrst value

returned by f or nil if f does not return any values.)

Expressions can also be built with arithmetic operators, relational operators, and logical oper-

ators, all of which are explained below.

2.5.1 Arithmetic Operators

Lua supports the usual arithmetic operators: the binary + (addition), - (subtraction), * (multipli-

cation), / (division), and ^ (exponentiation); and unary - (negation). If the operands are numbers,

or strings that can be converted to numbers (see §2.2.1), then all operations except exponentiation

have the usual meaning. Exponentiation calls a global function __pow; otherwise, an appropriate

metamethod is called (see §2.8). The standard mathematical library deﬁnes function __pow, giving

the expected meaning to exponentiation (see §5.5).

2.5.2 Relational Operators

The relational operators in Lua are

== ~= < > <= >=

These operators always result in false or true.

Equality (==) ﬁrst compares the type of its operands. If the types are diﬀerent, then the result

is false. Otherwise, the values of the operands are compared. Numbers and strings are compared

in the usual way. Objects (tables, userdata, threads, and functions) are compared by reference:

Two objects are considered equal only if they are the same object. Every time you create a new

object (a table, userdata, or function), this new object is diﬀerent from any previously existing

object.

You can change the way that Lua compares tables and userdata using the “eq” metamethod

(see §2.8).

The conversion rules of §2.2.1 do not apply to equality comparisons. Thus, "0"==0 evaluates

to false, and t[0] and t["0"] denote diﬀerent entries in a table.

The operator ~= is exactly the negation of equality (==).

The order operators work as follows. If both arguments are numbers, then they are compared

as such. Otherwise, if both arguments are strings, then their values are compared according to the

current locale. Otherwise, Lua tries to call the “lt” or the “le” metamethod (see §2.8).

2.5.3 Logical Operators

The logical operators in Lua are

and or not

Like the control structures (see §2.4.4), all logical operators consider both false and nil as false

and anything else as true.

The operator not always return false or true.

The conjunction op erator and returns its ﬁrst argument if this value is false or nil; otherwise,

and returns its second argument. The disjunction operator or returns its ﬁrst argument if this

value is diﬀerent from nil and false; otherwise, or returns its second argument. Both and and or

use short-cut evaluation, that is, the second operand is evaluated only if necessary. For example,

10 or error() -> 10

nil or "a" -> "a"

nil and 10 -> nil

false and error() -> false

false and nil -> false

false or nil -> nil

10 and 20 -> 20

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Lua 5.0编程参考手册

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