First Draft: opUnwrapIfTrue

[Richard (Rikki) Andrew Cattermole]

On 13/03/2026 3:18 AM, Ogion wrote:
> On Thursday, 26 February 2026 at 13:53:41 UTC, Richard (Rikki) Andrew 
> Cattermole wrote:
>> A new operator overload to allow if statements to automatically unwrap 
>> result types and ensure that the check is called prior to, similar to 
>> foreach statements support of ranges.
> 
> We have a proposed tuple unpacking syntax[1] in this form:
> 
> ```D
> Tuple!int result = tuple(99);
> (int value) = result;
> assert(value == 99);
> 
> ```
> 
> We could use the same syntax for unwrapping optional types. This 
> requires some additional rules:
> 1. If the type has a boolean value, it is checked before unpacking. If 
> the check fails:
> 1.1. If the unpacking declaration is in `if` statement, execution takes 
> the `else` branch (if exists).
> 1.2. If the unpacking declaration is in `foreach` statement, execution 
> continues to the next iteration.
> 1.3. Otherwise, an Error is thrown.
> 
> ```D
> @mustuse
> struct Result(Type) {
>      private {
>          Type value;
>          bool haveValue;
>      }
> 
>      this(Type value) {
>          this.value = value;
>          this.haveValue = true;
>      }
> 
>      bool opCast(T:bool)() => haveValue;
> 
>      (Type) = value; // TupleDeclarator (see DIP1053)

DIP1053 did not provide this "TupleDeclarator".
Right now that isn't a thing.

I'm inclined to say that with ``opUnwrapIfTrue`` it could return a 
tuple, that then is supported in the condition. ``If`` statements in 
grammar have their own rules for var declarations so some more work is 
required for it to work.