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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface-zh.html" > 译者序< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" class = "active" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.<
2022-08-04 06:59:33 +00:00
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2023-06-26 17:46:27 +00:00
< li > < em > 凹语言(专为 WebAssembly 设计): < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
< li > < em > KCL 配置语言(Rust): < a href = "https://github.com/kcl-lang/kcl" > https://github.com/kcl-lang/kcl< / a > < / em > < / li >
< / ul >
2022-08-04 06:59:33 +00:00
< hr >
< h2 id = "24-赋值" > < a class = "header" href = "#24-赋值" > 2.4. 赋值< / a > < / h2 >
< p > 使用赋值语句可以更新一个变量的值，最简单的赋值语句是将要被赋值的变量放在=的左边，新值的表达式放在=的右边。< / p >
< pre > < code class = "language-Go" > x = 1 // 命名变量的赋值
*p = true // 通过指针间接赋值
person.name = " bob" // 结构体字段赋值
count[x] = count[x] * scale // 数组、slice或map的元素赋值
< / code > < / pre >
< p > 特定的二元算术运算符和赋值语句的复合操作有一个简洁形式，例如上面最后的语句可以重写为：< / p >
< pre > < code class = "language-Go" > count[x] *= scale
< / code > < / pre >
< p > 这样可以省去对变量表达式的重复计算。< / p >
< p > 数值变量也可以支持< code > ++< / code > 递增和< code > --< / code > 递减语句（译注：自增和自减是语句，而不是表达式，因此< code > x = i++< / code > 之类的表达式是错误的）：< / p >
< pre > < code class = "language-Go" > v := 1
v++ // 等价方式 v = v + 1；
v-- // 等价方式 v = v - 1；
< / code > < / pre >
< h3 id = "241-元组赋值" > < a class = "header" href = "#241-元组赋值" > 2.4.1. 元组赋值< / a > < / h3 >
< p > 元组赋值是另一种形式的赋值语句，它允许同时更新多个变量的值。在赋值之前，赋值语句右边的所有表达式将会先进行求值，然后再统一更新左边对应变量的值。这对于处理有些同时出现在元组赋值语句左右两边的变量很有帮助，例如我们可以这样交换两个变量的值：< / p >
< pre > < code class = "language-Go" > x, y = y, x
a[i], a[j] = a[j], a[i]
< / code > < / pre >
< p > 或者是计算两个整数值的的最大公约数（ ） （ ： ， ， ） ： < / p >
< pre > < code class = "language-Go" > func gcd(x, y int) int {
for y != 0 {
x, y = y, x%y
}
return x
}
< / code > < / pre >
< p > 或者是计算斐波纳契数列（ ） ： < / p >
< pre > < code class = "language-Go" > func fib(n int) int {
x, y := 0, 1
for i := 0; i < n; i++ {
x, y = y, x+y
}
return x
}
< / code > < / pre >
< p > 元组赋值也可以使一系列琐碎赋值更加紧凑（译注: 特别是在for循环的初始化部分） ， < / p >
< pre > < code class = "language-Go" > i, j, k = 2, 3, 5
< / code > < / pre >
< p > 但如果表达式太复杂的话，应该尽量避免过度使用元组赋值；因为每个变量单独赋值语句的写法可读性会更好。< / p >
< p > 有些表达式会产生多个值，比如调用一个有多个返回值的函数。当这样一个函数调用出现在元组赋值右边的表达式中时（译注：右边不能再有其它表达式），左边变量的数目必须和右边一致。< / p >
< pre > < code class = "language-Go" > f, err = os.Open(" foo.txt" ) // function call returns two values
< / code > < / pre >
< p > 通常， ， ， ， （ ） （ ） （ < / p >
< pre > < code class = "language-Go" > v, ok = m[key] // map lookup
v, ok = x.(T) // type assertion
v, ok = < -ch // channel receive
< / code > < / pre >
< p > 译注： （ ） （ ） （ ） ， ， ， ， ， （ ） ： < / p >
< pre > < code class = "language-Go" > v = m[key] // map查找，
v = x.(T) // type断言，
v = < -ch // 管道接收，失败时返回零值（阻塞不算是失败）
_, ok = m[key] // map返回2个值
_, ok = mm[" " ], false // map返回1个值
_ = mm[" " ] // map返回1个值
< / code > < / pre >
< p > 和变量声明一样，我们可以用下划线空白标识符< code > _< / code > 来丢弃不需要的值。< / p >
< pre > < code class = "language-Go" > _, err = io.Copy(dst, src) // 丢弃字节数
_, ok = x.(T) // 只检测类型，忽略具体值
< / code > < / pre >
< h3 id = "242-可赋值性" > < a class = "header" href = "#242-可赋值性" > 2.4.2. 可赋值性< / a > < / h3 >
< p > 赋值语句是显式的赋值形式， ： ， ， （ < / p >
< pre > < code class = "language-Go" > medals := []string{" gold" , " silver" , " bronze" }
< / code > < / pre >
< p > 隐式地对slice的每个元素进行赋值操作， ： < / p >
< pre > < code class = "language-Go" > medals[0] = " gold"
medals[1] = " silver"
medals[2] = " bronze"
< / code > < / pre >
< p > map和chan的元素， ， < / p >
< p > 不管是隐式还是显式地赋值，在赋值语句左边的变量和右边最终的求到的值必须有相同的数据类型。更直白地说，只有右边的值对于左边的变量是可赋值的，赋值语句才是允许的。< / p >
< p > 可赋值性的规则对于不同类型有着不同要求， ， ： ， （ < / p >
< p > 对于两个值是否可以用< code > ==< / code > 或< code > !=< / code > 进行相等比较的能力也和可赋值能力有关系：对于任何类型的值的相等比较，第二个值必须是对第一个值类型对应的变量是可赋值的，反之亦然。和前面一样，我们会对每个新类型比较特殊的地方做专门的解释。< / p >
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