Review of DIP53

[Timon Gehr]

On 02/03/2014 01:58 AM, Andrei Alexandrescu wrote:
>
> Overall, I'm not clear what DIP53 does.

It removes the concept of const constructors and inout constructors from 
the language. The old const constructor syntax is then used to introduce 
a new feature that is very similar to inout constructors (the unique 
constructor) but requires special type checking rules for 
const-qualified data. It mostly removes features. Eg, the following code 
will break:

auto foo(const(int)[] x){
     struct S{
         int[] x;
         this(int y)const{ this.x=x; }
     }
     // ...
}

Some new code that wouldn't have been possible to write in an analogous 
way before:

struct S{
     int x;
     int[] y;
     this(int delegate(inout(int)[]) dg, inout(int)[] x)const{
         this.x=dg(x);
         this.y=[this.x];
     }
}

void main(){
     immutable s = S(x=>x[0],[1]);
     auto s = S((immutable x)=>x[0],cast(immutable)[2]);
}

Whatever strange class of new use cases DIP53 actually enables is fully 
covered by multiple inout-qualifiers as discussed in my previous post.