Chapter 6

Language Features

6.1 Conditional Compilation..................................

Haxe allows conditional compilation by using#if,#elseifand#elseand checking forcom-

piler flags.

Definition: Compiler Flag

A compiler flag is a configurable value which may influence the compilation process. Such

a flag can be set by invoking the command line with-D key=valueor just-D key, in

which case the value defaults to"1". The compiler also sets several flags internally to pass

information between different compilation steps.

This example demonstrates usage of conditional compilation:
1 class ConditionalCompilation {
2 public static function main(){
3 #if !debug
4 trace("ok");
5 #elseif (debug_level > 3)
6 trace(3);
7 #else
8 trace("debug level too low");
9 #end
10 }
11 }

Compiling this without any flags will leave only thetrace("ok");line in the body of the

mainmethod. The other branches are discarded while parsing the file. As a consequence, these

branches must still contain valid Haxe syntax, but the code is not type-checked.

The conditions after#ifand#elseifallow the following expressions:

• Any identifier is replaced by the value of the compiler flag by the same name. Note that
  -D some-flagfrom command line leads to the flagssome-flagandsome_flagto be
  defined.


• The values ofString,IntandFloatconstants are used directly.


• The boolean operators&&(and),||(or) and!(not) work as expected.