What's wrong with:

#define since(x) if(assert(x), 1)

(assert is required to expand to a void expression.)

Sensible standards requirements spoil all my fun ("you insensitive clod"). My technique, however, is extensible to other similar situations in which that guarantee isn't present :-P

*snap*

I was thinking (and I've not been a C++ programmer for almost a decade(:

#ifdef NDEBUG
#define since(cond) if (0) ; else
#else
#define since(cond) if (!(cond)) { assert(0); } else
#endif

Why does it matter what assert() returns?

As a side note, since() plays merry hell with emacs's formatting…

This could be fixed by hacking c-block-stmt-2-kwds in cc-langs.el, I think. But definitely a point against, yes.

It's sufficiently simple that you might just type it out rather than using a macro anyway.

The important point is that it expands to an expression, rather than (for instance) an if statement.

We want

if (foo)  handle_foo();
else if (bar)  handle_bar();
else since (baz)  handle_baz();
else since (quuz)  handle_quux();

to give a compile error.

Better example if the second since is an if.

gcc -Wunreachable-code -Werror

Or perhaps: #define since(x) if(assert(x),0);else (though I've not thought about this very hard yet).