PreferAtProvides

Prefer @Provides methods over the binding DSL

Many usages of the DSL are unclear to readers who are not Guice experts. Things like scoped bindings behave in ways that are easy to misunderstand where the @Provides implementation is more clear.

Consider this example:

bind(Foo.class).to(FooImpl.class).in(Singleton.class);
bind(Foo2.class).to(FooImpl.class).in(Singleton.class);

Will Foo and Foo2 bind to the same instance of FooImpl? That depends on whether FooImpl is annotated with @Singleton, which readers can't discern from looking at the DSL. If it is annotated then there will be one common instance, if not there will be two separate instances, despite the use of Singleton scopes.

Binding generic types can similarly be opaque and confusing when expressed with the DSL, but are very clear in @Provides methods.

That said, there are times where the DSL version is more readable than the equivalent providers. For instance a simple bind(Foo.class).to(FooImpl.class); statement is less boilerplate than the equivalent @Provides method. Readability and clarity should be the primary concern when choosing between different approaches.