Support multiple keys within Map Multibindings

It would be useful if when declaring a binding into a map, we could specify that one binding should be available under multiple keys.

Something like:

@Binds
@IntoMap
@TypeKey(Type.FOO)
@TypeKey(Type.BAR)
abstract Handler bindFooBarHandler(FooBarHandler handler);

or

@Binds
@IntoMap
@TypeKeys({Type.FOO, Type.BAR})
abstract Handler bindFooBarHandler(FooBarHandler handler);

Right now this can be accomplished with multiple @Binds methods within a module, which is a little verbose.

[ronshapiro]

these annotations should have SOURCE retention

SOURCE retention will not always work if the module is in a different compilation from the @Component that installs the module. But this is a point, just wanted to correct the record.

[devindi]

Hi guys,

I tried to use repeatable annotations from java 8 and I faced with issue.

Firstly I defined my custom annotation as map key like this (from tutorial):

enum MyEnum {
  ABC, DEF;
}

@MapKey
@interface MyEnumKey {
  MyEnum value();
}

After that I tried to bind same object to a few keys:

@Provides @IntoMap
  @MyEnumKey(MyEnum.ABC)
  @MyEnumKey(MyEnum.DEF)
  static String provideAbcOrDefValue() {
    return "value for ABC or DEF";
  }

Compiler said me that I should mark my annotation with Repeatable one This annotation this available since API level 24 so I can’t use multiple keys in my project.

Even in 2k19 we should support devices with API level 19 or even API level 17 so it would be great to support multiple keys from dagger’s side.