Go中的别名类型之间的转换是否创建副本？ [英] Does convertion between alias types in Go create copies?

问题描述

示例：

  type MyString string 
 var s =非常长的字符串
 var ms = MyString（s）
 var s2 =字符串
  

ms 或 s2 s 的完整副本 []字节（一个或多个））？或者他们只是一个字符串结构副本（它保留了一个指针的实际价值）？
如果我们将此函数传递给一个函数，该怎么办？例如：

  func foo（s MyString）{
 ... 
} 
 foo （毫秒（s））//我们在这里复制s吗？ 
  

解决方案

规范：转换：
$ b

具体规则适用于（非-constant）在数字类型之间或在字符串类型之间进行转换。这些转换可能会改变 x 的表示并导致运行时成本。 所有其他转换只会改变类型，但不会改变 x 的表示。

因此，如果转换为和来自您的自定义类型的基础类型不会创建副本。

当您将值传递给函数或方法，复制并传递。如果将字符串传递给一个函数，只会描述字符串的结构被复制并传递，因为 string s是不可变的。

如果传递一个切片（切片也是描述符），情况也是如此。传递片段将创建片段描述符的副本，但它将引用相同的基础数组。

Example:

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

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)? What if we are passing this to a function? Eg:

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

解决方案

Spec: Conversions:

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.

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

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.

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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