Re: Ada.Locales pseudo-string types

["J-P. Rosen" <rosen@adalog.fr>]

Le 08/08/2012 09:37, Niklas Holsti a �crit :

> But we are talking about explicitly requested type conversions, not
> implicit type equivalence. As I understood it, at least.
Yes, or more precisely, about the special rules for array conversions,
which are allowed if the types are structurally "close enough".
> 
>>> For a value conversion,
>>> the default could be to convert element by element, and the compiler
>>> could then optimize this conversion based on what it can deduce
>>> statically about the matching of the source and target subtypes.
>>
>> Could be interesting when elements themselves are arrays of discriminated
>> record subtypes constrained via discriminants with array components again
>> constrained etc.
> 
> Sure, but this should not require much new intelligence in the compiler.
> An array type conversion of the form A1 := A1_Type(A2); could just as
> well be written as an explicit loop with explicit element-by-element
> conversions, A1(I) := A1_Element_Type(A2(I)). A compiler could do this
> expansion internally, giving code that is legal today and which the
> compiler should already be able to compile.
> 
That's the whole point: a possible costly loop implicitely generated by
the compiler. The design choice was to /not/ hide this, i.e. allow array
conversions only when no extra code was required.

You are free to disagree with that design choice, of course...

-- 
J-P. Rosen
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