6.5 String Interpolation

With Haxe 3 it is no longer necessary to manually concatenate parts of a string due to the introduction of String Interpolation. Special identifiers, denoted by the dollar sign $ within a String enclosed by single-quote ' characters, are evaluated as if they were concatenated identifiers:

var x = 12;
// The value of x is 12
trace('The value of x is $x');

Furthermore, it is possible to include whole expressions in the string by using ${expr}, with expr being any valid Haxe expression:

var x = 12;
// The sum of 12 and 3 is 15
trace('The sum of $x and 3 is ${x + 3}');

String interpolation is a compile-time feature and has no impact on the runtime. The above example is equivalent to manual concatenation, which is exactly what the compiler generates:

trace("The sum of " + x +
  " and 3 is " + (x + 3));

Of course the use of single-quote enclosed strings without any interpolation remains valid, but care has to be taken regarding the $ character as it triggers interpolation. If an actual dollar-sign should be used in the string, $$ can be used.

Trivia: String Interpolation before Haxe 3

String Interpolation has been a Haxe feature since version 2.09. Back then, the macro Std.format had to be used, being both slower and less comfortable than the new string interpolation syntax.