Re: How to Emulate C++ Macro with Static Local Variable?

[Stephen Leake <Stephe.Leake@nasa.gov>]

taashlo@sandia.gov writes:

> What happens is that when you do this:
> 
> BAR(10);
> 
> it expands to this:
> 
> if (1) {
>   static s t_;
>   bar(&t_, 10);
> } else ((void)0);
> 
> This, in effect, creates a (hidden) static local variable for each call
> to bar().  This static variable (actually a structure, t_) is used to
> cache information for each unique call to bar() such that subsequent
> calls from that location can be processed *much* faster.

Just declare each "hidden static" variable directly, and call 'bar'. 

Yes, it's a few more lines of code, but it's worth it!

> for (int i = 0; i < 55; ++i) {
>    switch (wozit()) {
>       case 1: BAR(10); break;
>       case 2: BAR(20); break;
>       case 3: BAR(30); break;
>    }
> }

This would become:

package foo
    t_1 : s;
    t_2 : s;
    t_3 : s;

procedure Something is
begin
    for i in 1 .. 54 loop
       case wozit is
       when 1 =>
           bar (t_1, 10);
       when 2 =>
           bar (t_2, 20);
       when 3 =>
           bar (t_3, 30);
       end case;
    end loop;
end Something;

end foo;

You may complain this is using "ugly global variables", and it is. So is the
C code. Using macros to hide doesn't really make it prettier :).

A better way is to make 't' part of a state object that is passed in
to Something, but that's left as an exercise for the reader.

-- 
-- Stephe