Go 中别名类型之间的转换是否会创建副本? [英] Does conversion between alias types in Go create copies?

问题描述

例子:

type MyString string 
var s = "very long string"
var ms = MyString(s)
var s2 = string(s)

ms 或 s2 是 s 的完整副本吗(就像使用 []byte(s))?或者它们只是一个字符串结构副本(将真实值保存在指针中)?

Are ms or s2 a full copy of s (as it would be done with []byte(s))? Or they are just a string struct copies (which keeps the real value in a pointer)?

如果我们将 this 传递给函数会怎样?例如:

What if we are passing this to a function? E.g.:

func foo(s MyString){
  ...
}
foo(ms(s))  // do we copy s here?

推荐答案

规范:转换:

特定规则适用于数字类型之间或字符串类型之间的(非常量)转换.这些转换可能会改变 x 的表示并产生运行时成本.所有其他转换只改变x的类型而不改变表示.

Specific rules apply to (non-constant) conversions between numeric types or to and from a string type. These conversions may change the representation of x and incur a run-time cost. All other conversions only change the type but not the representation of x.

因此，与自定义类型的基础类型相互转换不会复制它.

So converting to and from the underlying type of your custom type does not make a copy of it.

当您将值传递给函数或方法时，会制作并传递一个副本.如果将 string 传递给函数，则只会复制和传递描述 string 的结构，因为 string 是不可变的.

When you pass a value to a function or method, a copy is made and passed. If you pass a string to a function, only the structure describing the string will be copied and passed, since strings are immutable.

如果你传递一个切片也是如此(切片也是描述符).传递切片将复制切片描述符，但它会引用相同的底层数组.

Same is true if you pass a slice (slices are also descriptors). Passing a slice will make a copy of the slice descriptor but it will refer to the same underlying array.

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