Swift 里面的"_"是什么作用

[ufo22940268]

struct MyView: View {
    @Binding var a: Bool
    init(a: Binding<Bool> = .constant(true)) {
        _a = a
    }

    var body: some View {
        Text("MyView")
    }
}

stackoverflow

这里面的_a中的_是什么作用，我在文档上没有找到

[Procumbens]

https://stackoverflow.com/questions/30609636/what-does-an-underscore-before-a-swift-variable-mean/30609658

[ufo22940268]

@Procumbens 好像是两个事情，你看我的 snippet 里面定义的变量名是没有_开头的，但是赋值的时候就加上了_

[Nitroethane]

In Objective-C when you declare a property @synthesize would create the getter and setters for you automatically since clang 3.2. So, the default @synthesize for a property "foo" would look like this:

@synthesize foo = _foo

because of that _foo would then be the iVar. In other words you could have done the @synthesize yourself and called the iVar whatever you liked:

@synthesize foo = myiVarFoo

so in this case there is no "_"

So now in Swift from the documentation:

Swift unifies these concepts into a single property declaration. A Swift property does not have a corresponding instance variable, and the backing store for a property is not accessed directly.
So from the documentation it's clear that swift does not have a corresponding instance variable thus no need to have the "_" around anymore.


https://stackoverflow.com/a/24215607