Functor alias this

[Simen Kjærås]

On Wednesday, 6 June 2018 at 06:25:49 UTC, DaggetJones wrote:
> Hi, I'm wondering how I should approach supplying 
> functions/delegates around in D. I have option of using classes 
> where the function exists inside the class and to provide 
> different functionality different classes are created.
> Alternatively I could just pass the function directly around 
> without all the weight of the class.
>
> This led me to wonder if there is a way to combine the two 
> methods?
>
>
> With D's alias this would it be possible to have the user code 
> treat the function as a delegate but define the functions 
> actually in a class without any restrictions?
>
>
> import std.stdio;
>
> alias MyFunction = int delegate();
>
> class MyFunctor
> {
>    alias func this;
>    int MyData = 5;
>    int func() { return MyData; }
> }
>
>
>
> void bar(MyFunction foo) { writeln(foo()); }
>
> void main()
> {
>
> 	MyFunctor f = new MyFunctor();
> 	
> 	bar(&f.func);
>         // but not
>         // bar(f); or bar(&f);
> 	
> }
>
>
> But I would like to simply pass the class as if it were the 
> member func, which is what the alias this is suppose to provide.
>
> It seems D ignores the alias this in this case?

You'll need to provide a function that returns func. The way it's 
currently written, the alias this would basically translate to 
bar(f.func()):

class MyFunctor
{
    alias func2 this;
    int MyData = 5;
    int func() { return MyData; }
    auto func2() { return &func; }
}

--
   Simen