英文:
What does the interface function/"cast" actually do in golang?
问题
我对golang相对较新，我正在查看的项目中有这种模式重复了几次：
package foo
type Foo interface {
Bar() int
}
type foo struct {
}
func (f *foo) Bar() int {
return 42
}
func New() Foo {
// 为什么？
return Foo(&foo{})
}
如果我将最后一个函数中的返回语句替换为return &foo{}，一切都按照我预期的正常工作...如果我理解正确的话，这是一种鸭子类型。那么使用Foo(...)函数的目的是什么？当您在一个可能具有方法的类型中包装内置类型（如int）时，使用类型作为函数似乎是有效的。我对作者的意图很好奇。如果在语言规范中有涵盖到，我找不到它。
英文:
I'm relatively new to golang, and the project I'm looking at has this sort of pattern repeated several times:
package foo
type Foo interface {
Bar() int
}
type foo struct {
}
func (f *foo) Bar() int {
return 42
}
func New() Foo {
// why?
return Foo(&foo{})
}
If I replace the returns statement in the last function with return &foo{} everything works fine as I expected... it's duck typing if I understand it correctly. So what is the point of using the Foo(...) function? Using a type as a function seems to work when you're wrapping a built in type such as int in a type that probably has methods. I'm curious as to the author's intent here. If it's covered in the language spec I was unable to find it.
答案1
得分: 3
表达式Foo(x)是一个转换。这里不需要进行转换，因为*foo可以赋值给Foo。代码应该写成：
func New() Foo {
return &foo{}
}
英文:
The expression Foo(x) is a conversion. The conversion is not needed here because a *foo is assignable to a Foo. The code should be written as:
func New() Foo {
return &foo{}
}
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