Conditional compilation

Conditional compilation lets you write code that adapts to statically known information like presence or absence of other mods. For example, you might want to use a feature from another mod, but only if the user has that mod installed. Or you might want to avoid a conflict with another mod by changing your code depending on whether that mod is present or not.

To use conditional compilation, you need to use the @if annotation followed by a condition before the code that you want to include or skip. Here’s a simple example:

module My.Mod
// This line will only import Other.Mod if it exists.
@if(ModuleExists("Other.Mod"))
import Other.Mod.*

// This function has two versions: one for when Other.Mod exists and one for 
// when it doesn't.
// The imports from Other.Mod are only valid in the first version, because 
// they depend on the condition.
@if(ModuleExists("Other.Mod"))
func Testing() -> Int32 {
    return 1;
}
@if(!ModuleExists("Other.Mod"))
func Testing() -> Int32 {
    return 2;
}

// This method wrapper/replacement only take effect if Other.Mod doesn't exist.
@if(!ModuleExists("Other.Mod"))
@wrapMethod(PlayerPuppet)
protected cb func OnGameAttached() -> Bool {
  Log("I'm in a wrapper");
  wrappedMethod();
}

// Class is defined only if Other.Mod exists.
@if(ModuleExists("Other.Mod"))
public class MySettings {
  // Same as Testing() above, but for fields of a class.
  @if(ModuleExists("Other.Mod"))
  let resolution: Vector2;
  @if(!ModuleExists("Other.Mod"))
  let resolution: String;
  
  // Same as Testing() above, but for methods of a class.
  @if(ModuleExists("My.Mod.Test"))
  public func GetMode() -> CName {
    return n"Debug";
  }
  @if(!ModuleExists("My.Mod.Test"))
  public func GetMode() -> CName {
    return n"Release";
  }
}

The condition in the @if annotation can only consist of:

• true or false

• logical operators (&&, ||, !, ?:)

• the ModuleExists function, which returns true if a mod name exists and false otherwise

Since v0.5.18, you can use @if annotation on class members (fields and methods) like in the example above.