Re: What is the purpose of Vector.Query_Element?

["Randy Brukardt" <randy@rrsoftware.com>]

"EGarrulo" <egarrulo@gmail.com> wrote in message 
news:ca22434f-8216-4cbd-a4c0-46fea8e6cc98@googlegroups.com...
> The package that defines Vector provides this procedure:
>
> procedure Query_Element
>  (Container : in Vector;
>   Index : in Index_Type;
>   Process : not null access procedure (Element : in Element_Type));
>
> Why is this procedure provided?  Isn't `Query_Element (Vector, Index, 
> Process'Access)` the same as `Process (Element (Vector, Index))`?

Sure, if you don't care about performance they're the same. But a function 
result is a copy of the element ("Element" is a function), whereas 
Query_Element can pass the element by reference (and will for most types 
that aren't by-copy); in that case it is directly referenced in place. For 
large elements (say, like other containers), the overhead of copying could 
be considerable. OTOH, if the element is a by-copy type, there is no 
difference. So Query_Element is a specialized need. Besides, for Ada 2012, 
you probably ought to be using the indexing syntax and not use either of 
these.

                                Randy.