Ever wanted to:
1) Set default binding in a library or framework that users can change?
2) Inject something into a library or framework that isn't required, but
would be better if a user could set it?
3) Inject an optional value into a constructor?
OptionalBinder lets you do that. Christian just pushed out some of our
recent internal changes, including the introduction of OptionalBinder to
the multibindings extension.
Some example usage:
1) Setting a default binding that a user can override:
Library: *OptionalBinder.newOptionalBinder(binder(), Foo.class)*
* .setDefault().to(DefaultFoo.class);*
At this point, code can inject '*Foo*' (or *Optional<Foo>)*, and will
get a *DefaultFoo.*
User: *OptionalBinder.newOptionalBinder(binder(), Foo.class)*
* .setBinding().to(CustomFoo.class);*
Once a user calls setBinding(), injections of *Foo* (or
*Optional<Foo>)* will
start providing *CustomFoo* instead.
2) Setting a binding that isn't required (e.g, no default value), but a
user can supply.
Library: *OptionalBinder.newOptionalBinder(binder(), Foo.class);*
At this point, code *can't* inject *Foo* -- it will fail saying the
binding isn't supplied. Code *can* (and should) inject *Optional<Foo>*,
though, and the optional will be absent.
User: *OptionalBinder.newOptionalBinder(binder(), Foo.class)*
* .setBinding().to(CustomFoo.class);*
Once a user calls setBinding(), *Optional<Foo>* will be present and
supply the *CustomFoo*. Also, *Foo* can be directly injected now (although
only user could should do that, since the user code is the only part that
guarantees the binding will be there -- library code should still inject the
* Optional<Foo>*).
Please report back if you have any issues or suggestions for improvement.
Thanks!
sam
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