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Conditional Compilation Sample ​

Vala supports compile-time conditionals with #if / #elif / #else / #endif. This is not a full C-style macro preprocessor: it only selects code at compile time based on symbols defined with valac -D.

Adapted from the archived Conditional Compilation Sample page.

See Language Features and Introductory Samples for the full set.

vala
void main () {

#if ( FOOBAR || FOO || BAR ) && (FOOBAR == FOO && FOO == BAR)
    message ("FOOBAR == FOO == BAR");
#endif

#if ! NOFOO && (FOOBAR || (FOO && BAR))
    message ("FOOBAR");
#elif FOO && ! NOFOO
    message ("FOO");
#elif BAR && ! NOFOO
    message ("BAR");
#elif NOFOO
#if FOOBAR || (FOO && BAR)
    message ("NOFOO FOOBAR");
#else
    message ("NOFOO");
#endif
#else
    message ("Nothing relevant defined");
#endif

}

Compile and run ​

Try different -D combinations:

shell
valac -D FOOBAR conditional-compilation.vala
./conditional-compilation

valac -D FOO -D BAR conditional-compilation.vala
./conditional-compilation

valac -D FOO -D BAR -D FOOBAR -D NOFOO conditional-compilation.vala
./conditional-compilation