英文:
How do go's len() and make() functions work?
问题
Go语言中的len()和make()函数是如何工作的？由于该语言不支持泛型和函数重载，我不明白如何实现func len(v Type) int和func make(Type, size IntegerType) Type这两个函数。
我在Go的源代码中找不到这个函数，我找到的最接近的是这个链接。
英文:
How do go's len() and make() functions work? Since the language lacks support for both generics and function overloading I don't see how func len(v Type) int is possible. The same goes for func make(Type, size IntegerType) Type.
I can't seem to find the function in the go source, the closest I've managed to find is this
答案1
得分: 18
len和make函数是语言规范的一部分，并内置于编译器中。内置函数的运行时支持在runtime包中。
文件builtin.go仅用于文档目的，不会被编译。
英文:
The len and make functions are part of the language specification and built-in to the compiler. Runtime support for built-in functions is in the runtime package.
The file builtin.go is used for documentation only. It's not compiled.
答案2
得分: 1
由于Go语言的严格类型，编译器总是知道你传递给len函数的类型，因此它会根据不同的类型调用不同的函数，这在编译时可以确定。在大多数情况下，你试图获取切片的长度，此时len函数只需要返回该切片结构体的len字段（因为切片实际上是一个结构体）；字符串也是同样的道理。
编译器有各种各样的技巧，由编译器生成的汇编代码很少遵循你输入的完全相同的逻辑。
英文:
Because of Go's strict types, the compiler always knows what type you are passing to the len function and so it goes to a different function for different types, which can be determined at compile-time. In most cases you are attempting to get the length of a slice, in which case the len function only need return the len field for that slice's struct (since a slice is really a struct); same for a string.
Compilers have all kinds of tricks, the assembly code generated by the compiler rarely follows the exact same logic you typed.
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