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December 10, 2010
Comparing template alias parameters
Given an index structure like this:

struct Index( alias arr ) if ( is( typeof( arr ) t : U[], U ) ) {
    private size_t idx;
    @property pure nothrow size_t get( ) const {
        return idx;
    }
    alias get this;

    invariant( ) {
        assert( idx < arr.length );
    }

    this( size_t value ) {
        idx = value;
    }

    Index opAssign( size_t value ) {
        idx = value;
        return this;
    }
}

would it be possible to do something akin to this:

void foo( T )( T[] arr, Index!arr a ) {
}

void bar( ) {
    int[] a = [1,2,3];
    Index!a idx;
    foo( a, idx ); // ensures idx is a valid index for a
}


Somewhat trivial an application, as this could easily be tested
with an in clause, but imagine that ( arr is Index!(arr).arr )
has to be true.


-- 
Simen
December 13, 2010
Re: Comparing template alias parameters
Simen kjaeraas <simen.kjaras@gmail.com> wrote:

> Given an index structure like this:
>
> struct Index( alias arr ) if ( is( typeof( arr ) t : U[], U ) ) {
>      private size_t idx;
>      @property pure nothrow size_t get( ) const {
>          return idx;
>      }
>      alias get this;
>
>      invariant( ) {
>          assert( idx < arr.length );
>      }
>
>      this( size_t value ) {
>          idx = value;
>      }
>
>      Index opAssign( size_t value ) {
>          idx = value;
>          return this;
>      }
> }
>
> would it be possible to do something akin to this:
>
> void foo( T )( T[] arr, Index!arr a ) {
> }
>
> void bar( ) {
>      int[] a = [1,2,3];
>      Index!a idx;
>      foo( a, idx ); // ensures idx is a valid index for a
> }
>
>
> Somewhat trivial an application, as this could easily be tested
> with an in clause, but imagine that ( arr is Index!(arr).arr )
> has to be true.


Nobody? Meh.

-- 
Simen
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