Re: Misleading Compiler Warning

[Jeffrey Carter <jrcarter@acm.org>]

Volkert wrote:
> pack.adc:9:03: warning: in instantiation at Gen.adc:4
> pack.adc:9:03: warning: value not in range of type "Standard.Integer"
> pack.adc:9:03: warning: "Constraint_Error" will be raised at run time

This is an unusual warning. However, I think some warning is a good 
idea; see below.

> 
> generic
>    type S is private;
> package Gen is
> 
>    generic
>       type T is range <>;
>    package Inner_Gen is
>       procedure Do_It;
>    end Inner_Gen;
> 
> end Gen;
> 
> ---
> 
> package body Gen is
>    
>    package body Inner_Gen is
>       type B is array(T) of Boolean;
>       pragma Pack(B);
>       type C is array (0 .. 100) of B;
> 
>       procedure Do_It is
>         O : C;
>       begin
>         O(1)(0) := False;

                ^ Here you assume that 0 is a value of the formal type T

>       end;
>    
>    end;
> 
> end Gen;

There is no guarantee that zero is a value of the actual type used for 
the formal type T; a (sub)type with a 'First of one is very likely. 
While the warning you got is not very good, some sort of warning seems 
in order here.

-- 
Jeff Carter
"I've got to stay here, but there's no reason
why you folks shouldn't go out into the lobby
until this thing blows over."
Horse Feathers