[swift-evolution] Operator implementation inside struct/class body

[Charles Srstka]

> On Jan 30, 2016, at 11:03 PM, Vanderlei Martinelli via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Since the first public betas I’d like to know why operator implementation have to be written outside the body of its owner.
> 
> Take as example the code:
> 
> protocol MyEquatable {
>     @warn_unused_result
>     func ==(lhs: Self, rhs: Self) -> Bool
> }
> 
> struct MyStruct: MyEquatable {
>     let foo: String
>     let bar: String
> }
> 
> func ==(lhs: MyStruct, rhs: MyStruct) -> Bool {
>     return lhs.foo == rhs.foo && lhs.bar == rhs.bar
> }
> 
> Why we cannot write:
> 
> protocol MyEquatable {
>     @warn_unused_result
>     func ==(lhs: Self, rhs: Self) -> Bool
> }
> 
> struct MyStruct: MyEquatable {
>     let foo: String
>     let bar: String
>     
>     func ==(lhs: MyStruct, rhs: MyStruct) -> Bool {
>         return lhs.foo == rhs.foo && lhs.bar == rhs.bar
>     }
> 
> }
> 
> Any thoughts?
> 
> 
> -Van

+1. I’ve been meaning to write up something about this for some time. The thing I’d change is to include only the right-hand side as an argument, and use ‘self’ to refer to the left-hand side:

struct MyStruct: MyEquatable {
    let foo: String
    let bar: String
    
    func ==(other: MyStruct) -> Bool {
        return self.foo == other.foo && self.bar == other.bar
    }
}

Charles

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