Re: Vector (container) initialization: the schizophrenic ampersand

[Adam Beneschan <adam@irvine.com>]

On Thursday, May 17, 2012 1:20:31 PM UTC-7, marius63 wrote:
> Shouldn't this be the right idiom to initialize a vector (container) with literals:
> 
> use My_Vectors;
> V : My_Vectors.Vector := Element1 & Element2 & Element3;
> 
> Looks nice, but does not compile (with GNAT), because the compiler cannot make a decision on which "&" function to use where. Is there a way to give precedence to one of the "&" functions? Or some other nice solution? Thanks.
> 
> /*
> My current solution is to rename one of the functions:
> 
> use My_Vectors;
> 
> function "+" (L : My_Vectors.Vector; R : My_Element_Type)
>    renames My_Vectors."&";
> 
> V : My_Vectors.Vector := Element1 & Element2 + Element3;
> 
> Not elegant at all.
> */

It compiled for me the first time I tried it, so I think we need more information, in particular what your element type is.  A complete example that compiles except for that error would be helpful.

Parentheses won't help.  The operator precedence rules mean that the expression is always interpreted as (Element1 & Element2) & Element3 regardless of what functions the operators refer to.  

If your element type is some sort of array, then there could be a conflict with the built-in array concatenation operator.  The solution might be

   V : My_Vectors.Vector := My_Vectors.Vector'(Element1 & Element2) & Element3;

to make it clear that the first "&" must be the one that returns a Vector.

                           -- Adam