Proposal: property 'fetch' for AA

[Oskar Linde]

eao197 skrev:
> Ruby's Hash has a handy method 'fetch'[1] which allows to extract value 
> from Hash or, if value is missed, use some default value:

> If D's AA would have property 'fetch' it would allow to write:
> 
> int[char] h;
> h[ 'a' ] = 1;
> auto a = h.fetch( 'a', 0 );
> auto b = h.fetch( 'b', 10 );
> 
> instead of:
> 
> V fetch(K,V)( V[K] h, K key, V default_value )
> {
>   if( key in h )
>     return h[key];
>   return default_value;
> }

A slightly different version I've been using:

T get(T,U)(T[U] aa, U key) {
         T* ptr = key in aa;
         if (ptr)
                 return *ptr;
         return T.init;
}

T get(T,U, int dummy = 1)(T[U] aa, U key, lazy T defaultValue) {
         T* ptr = key in aa;
         if (ptr)
         	return *ptr;
         return defaultValue;
}

and

T getCached(T,U)(T[U] aa, U key, lazy T computedValue) {
	T* ptr = key in aa;
	if (ptr)
		return *ptr;
	T val = computedValue;
	aa[key] = val;
	return val;
}

The latter one could probly use a better name, but the idea is to 
conveniently be able to use an AA as a cache for expensive computations.

/Oskar