$define/$Ifdef don't just take (name) identifiers.

They also take numbers, <strike>and expressions. </strike>

Well actually, numbers.
{$define 2}
{$IFDEF 2} .... {$ENDIF}

The below at first looked like expressions too (but as literal text) But like any directive, it parses until it has the directive (in this case the first ident "2" and ignores the rest "+1" as comment.

The below is just about the "2":
{$define 2+1}
{$IFDEF 1+2} not compiled {$ENDIF}
{$IFDEF 2+1} foo; {compiled} {$ENDIF}
{$IFDEF 2+ 1} foo; {compiled} {$ENDIF} // note the space

See also
https://forum.lazarus.freepascal.org/index.php/topic,72937.0.html

Seriously ?

The inventive ways by which people try to shoot themselves in the foot never cease to amaze me...

They do it with lots of enthusiasm, it seems :-)

Michael.

Ok, so the docs says defines a "name" or "symbol", it does not refer to "identifier". Which means I guess numbers are in that scope.

And I just realised, the above can be used with macros.

{$macro on}
{$define 0=1}
begin
   write(random(123) / 0);

should work ... ;)

I doubt this is intentional, but if it makes you happy...

Michael.

Il 07/12/25 10:05, Martin Frb via fpc-devel ha scritto:

The inventive ways by which people try to shoot themselves in the foot never cease to amaze me.

I'm afraid that too many people don't realize that a computer is not "intelligent". It's nothing but a stupid very fast calculator, provided of means to tell it what keys to strike, called "programs". If the program tells "if you find "0" strike key 1", it will do it.

Writing a compiler which blocks human stupidity is an hopeless goal. As Einstein stated, it's impossible, "because human intelligence has a limit, while human stupidity has none".

Giuliano