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tutorial:interface_injection

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tutorial:interface_injection [2025/11/10 03:38] – Add info on how to inject generic interfaces earthcomputertutorial:interface_injection [2025/12/27 12:27] (current) – gauntrecluse
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 More specifically, you can create an interface, and then inject this interface into the class. More specifically, you can create an interface, and then inject this interface into the class.
 As result the target class will acquire all the methods of the interface, as if it always had them. As result the target class will acquire all the methods of the interface, as if it always had them.
-Interface injection is a compile time only feature, this means that a Mixin should also be used to implement the interface into the target class. 
  
 This is particularly useful for libraries, with this you can add new methods to existing classes and use them without the need of casting or reimplementing the interface every time. This is particularly useful for libraries, with this you can add new methods to existing classes and use them without the need of casting or reimplementing the interface every time.
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 <yarncode java [enable_line_numbers="false"]> <yarncode java [enable_line_numbers="false"]>
-Optional<class_3414> getBucketEmptySound$myMod()+Optional<class_3414> modid$getBucketEmptySound()
 </yarncode> </yarncode>
  
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 public interface BucketEmptySoundGetter { public interface BucketEmptySoundGetter {
- default Optional<class_3414> getBucketEmptySound$myMod() {+ default Optional<class_3414> modid$getBucketEmptySound() {
  return Optional.empty();  return Optional.empty();
  }  }
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 </yarncode> </yarncode>
  
-:!: The method body in the interface may not be used because it will be overridden by the mixin class. However, you must specify the method body, which means the method must be ''default''. You can make it return null or throw ''UnsupportedOperationException'', but you //cannot// make it abstract, such as ''Optional<yarn class_3414> getBucketEmptySound()'', or exceptions will be thrown when compiling!+:!: Even if the method body in the interface isn't supposed to be used because it will be overridden by the mixin class, you must still generally specify the method body, which means the method must be ''default''. You can make it return null or throw ''UnsupportedOperationException'', but you //cannot// make it abstract, such as ''Optional<yarn class_3414> modid$getBucketEmptySound()'', or exceptions will be thrown when compiling!
  
-ℹ️ It's highly recommended to add a dollar-character or underscore character with the mod name as the prefix or suffix of the method name, in order to avoid method name conflict with other mods.+ℹ️ If implementing the method with an interface, it's highly recommended to add a dollar-character or underscore character with the mod name as the prefix or suffix of the method name, in order to avoid method name conflict with other mods.
  
 ===== Step 2: Implement the Interface with a Mixin ===== ===== Step 2: Implement the Interface with a Mixin =====
  
-Now you need to implement this interface into ''<yarn net.minecraft.class_3609>'' with a mixin implementing the interface:+The class tweaker step below on its own will be enough if you only want to implement the interface (for example, for marker interfaces, or where you have the whole implementation in default methods). However, you need to implement this interface on a mixin to ''<yarn net.minecraft.class_3609>'' if you want to implement any methods without providing the implementation in a default method:
  
 <yarncode java [enable_line_numbers="false"]> <yarncode java [enable_line_numbers="false"]>
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 abstract class MixinFlowableFluid implements BucketEmptySoundGetter { abstract class MixinFlowableFluid implements BucketEmptySoundGetter {
  @Override  @Override
- public Optional<class_3414> getBucketEmptySound$myMod() {+ public Optional<class_3414> modid$getBucketEmptySound() {
      //This is how to get the default sound, copied from BucketItem class.      //This is how to get the default sound, copied from BucketItem class.
      return Optional.of(((class_3609) (Object) this).method_15791(class_3486.field_15518) ? class_3417.field_15010 : class_3417.field_14834);      return Optional.of(((class_3609) (Object) this).method_15791(class_3486.field_15518) ? class_3417.field_15010 : class_3417.field_14834);
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 </yarncode> </yarncode>
  
-===== Step 3: Inject the Interface in ''fabric.mod.json'' =====+ 
 +===== Step 3: Inject the Interface in the class tweaker =====
  
 Lastly you need to inject the interface into ''<yarn net.minecraft.class_3609>''. Lastly you need to inject the interface into ''<yarn net.minecraft.class_3609>''.
-The following snippet can be added to your ''fabric.mod.json'' file to add one or more interfaces to the ''<yarn net.minecraft.class_3609>'' class.+The following snippet can be added to your class tweaker file to add one or more interfaces to the ''<yarn net.minecraft.class_3609>'' class. 
 +Follow the [[tutorial:accesswidening|access widening tutorial]] for how to create a class tweaker.
 Note that all class names here must use the "internal names" that use slashes instead of dots (''path/to/my/Class''). Note that all class names here must use the "internal names" that use slashes instead of dots (''path/to/my/Class'').
  
-<code json fabric.mod.json [enable_line_numbers="false"]> +<code - mymod.classtweaker [enable_line_numbers="false"]> 
-{ +classTweaker v1 named 
- "custom": { + 
- "loom:injected_interfaces": { +inject-interface net/minecraft/fluid/FlowableFluid net/fabricmc/example/BucketEmptySoundGetter
- "net/minecraft/class_3609": ["net/fabricmc/example/BucketEmptySoundGetter"] +
- } +
- } +
-}+
 </code> </code>
  
-:!: Sometimes, your interface injections may need to include the ''$'' symbol, but the Groovy template processor may interpret this as a template variable if you are replacing variables (such as ''${version}'') in your ''fabric.mod.json''. A workaround for this is to use the Unicode escape for ''$'', which is ''\u0024''.+:!: To make your interface injection visible to other mods depending on your mod (if you are writing a library mod), use ''transitive-inject-interface'' instead of ''inject-interface''.
  
 ==== Generic interfaces ==== ==== Generic interfaces ====
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 Here is a full example using generics: Here is a full example using generics:
-<code json fabric.mod.json [enable_line_numbers="false"]> +<code - mymod.classtweaker [enable_line_numbers="false"]> 
-{ +classTweaker v1 named 
- "custom": { + 
- "loom:injected_interfaces": { +inject-interface net/minecraft/fluid/FlowableFluid net/fabricmc/example/MyGenericInterface<+TT;TU;>
- "net/minecraft/class_3609": ["net/fabricmc/example/MyGenericInterface<+TT;TU;>"] +
- } +
- } +
-}+
 </code> </code>
 which would generate the implementation: which would generate the implementation:
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 <yarncode java [enable_line_numbers="false"]> <yarncode java [enable_line_numbers="false"]>
-Optional<class_3414> sound = mytestfluid.getBucketEmptySound$myMod();+Optional<class_3414> sound = mytestfluid.modid$getBucketEmptySound();
 </yarncode> </yarncode>
  
tutorial/interface_injection.1762745926.txt.gz · Last modified: 2025/11/10 03:38 by earthcomputer