Rust的函数__Function

Functions are prevalent in Rust code. You’ve already seen one of the most important functions in the language: the main function, which is the entry point of many programs. You’ve also seen the fn keyword, which allows you to declare new functions._{函数在Rust代码中非常流行，你已经见过最重要的函数——main函数（许多编程语言的入口），你也见过fn关键字，其允许你用以声明一个新的函数。}

Rust code uses snake case as the conventional style for function and variable names, in which all letters are lowercase and underscores separate words. _{Rust代码以蛇形命名法来命名函数名和变量名，其形式由小写字母+下划线组成。}

fn main() {
    println!("Hello, world!");

    another_function();
}

// fn关键字 函数名 (形参列表) {函数体}
fn another_function() {
    println!("Another function.");
}

 Parameters_参数

We can define functions to have parameters, which are special variables that are part of a function's signature. _{我们可以给函数定义一些参数，这些指定的变量是函数签名的一部分。}When a function has parameters, you can provide it with concrete values for those parameters. _{当函数具有参数时，你可以为这些参数提供具体的值。}Technically, the concrete values are called arguments, but in casual conversation, people ten to use the words parameter and argument interchangeably for either the variables in a function's definition or the concrete values passed in when you call a funcion._{从技术上来讲，这些具体的值应称之为arguments，但日常称谓中，人们将parameter和argument混淆使用，来表示定义函数的参数parameter或调用函数时提供的参数argument。}

fn main() {
    another_function(5);
}

fn another_function(x: i32) {
    println!("The value of x is: {x}");
}

Statements and Expressions

Function bodies are made up of a series of statements optionally ending in an expression._{函数体由一系列语句+表达式结尾（可选）组成。} // 函数体由花括号包裹

statements: instructions that perform some action and do not return a value. // 执行某些操作的指令但不返回值

expressions: evaluate to a resultant value. // 返回值

// 有返回值函数
// fn func_name () -> type {body}
fn five() -> i32 {
    5
}

// 无返回值函数
fn main() {
    let x = five();

    println!("The value of x is: {x}");
}

fn main() {
    let x = plus_one(2);
    println!("The value of x is {x}");
}

// 此函数有返回值类型，因此最后一句必须为expressions
fn plus_one(x: i32) -> i32 {
//    x + 1; // 错误写法，编译报错
    x + 1 // 正确写法，表达式expressions不以分号';'结尾，语句statements需要有分号结尾
}