Re: Return statements and their scope - guideline

["Jeffrey R. Carter" <jrcarter@acm.org>]

Maciej Sobczak wrote:
> 
> I have found a coding guideline that allows return statements only in 
> the outermost scope in the subprogram - which is supposed to avoid 
> obscuring the control flow.
> 
> What is outermost scope in this context?
> 
> function F return Integer is
> begin
>   if Some_Condition then
>      return 0;   -- (1)
>   end if;
>   -- ...
>   declare
>     X : Integer;
>   begin
>     -- ...
>     return X;    -- (2)
>   end;
>   -- ...
>   return 7;      -- (3)
> end F;
> 
> Is (1) above in the outermost scope?

No. This is the rule in SPARK: You have to write

if Some_Condition then
    Result := 0;
else
    ...
    Result := ...;
end if;

return Result;

This makes the analysis easier. However, I've always felt

if Some_Condition then
    return 0;
end if;

is easier to read; if you're interested in the case where Some_Condition 
holds, then you don't have to read any further.

I wonder how such coding standards will deal with the extended return 
statement of Ada 0X.

-- 
Jeff Carter
"I blow my nose on you."
Monty Python & the Holy Grail
03