英文:
Length and capacity methods in slices
问题
阅读有关Golang中数组和切片的内容。
为什么要使用内置函数，如len和cap，而不是类似的切片对象方法？
if cap(slice) == len(slice) {
fmt.Println("slice is full!")
}
与
if slice.cap() == slice.len() {
fmt.Println("slice is full!")
}
为什么要污染全局命名空间？为什么不使用面向对象的风格？
此外，是否存在这样的方法，可以替代内置函数使用？
英文:
Reading about arrays and slices in Golang.
Why built-in functions like len and cap are used and not similar methods on slice objects?
if cap(slice) == len(slice) {
fmt.Println("slice is full!")
}
vs
if slice.cap() == slice.len() {
fmt.Println("slice is full!")
}
Why polluting the global namespace? Why not using object oriented style?
Also, do such methods exist and can they be used instead of built-in functions?
答案1
得分: 2
这个问题有一个常见问题解答，但是我来解释一下：
len()和cap()是内置函数，因为编译器能够理解它们。你不能自己替换它们，它们是核心语言的一部分，与方法不同，不要混淆它们。
在Go语言中，切片由三部分组成：长度、容量和指向底层内存的指针。例如，reflect包中的定义：
type SliceHeader struct {
Data uintptr
Len int
Cap int
}
len(x)只是从切片结构中读取长度，所以它相当于x.Len的简写形式，编译器能够理解并进行相应的优化。
英文:
There is a FAQ entry on this, but here is my take:
len() and cap() are built in functions because they are understood by the compiler. You can't make your own replacements - they are very much part of the core language in a way that methods aren't, and you shouldn't confuse them with methods.
In Go a slice is made of three things, a length, a capacity and a pointer to the underlying memory. Eg the definition from reflect
type SliceHeader struct {
Data uintptr
Len int
Cap int
}
All len(x) does is read the length from the slice structure, so it is shorthand for something like x.Len and the compiler understands that and optimises it accordingly.
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