Google Wire uses a code generation approach, that is it does compile time
dependency injection using go generate.
Two core notions:
- providers
- injectors
Providers produce a value, using plain Go code (e.g. a function). They can specify dependencies (e.g. parameters) and can also return errors.
A number of providers (and sets) can be grouped into a set:
At construction time, we want to create required values (in a suitable order) - this is done with an injector. The signature guides the process of creating the dependent values.
By default, the generated file is named:
wire_gen.go
And it is guarded by a build constraint:
//+build !wireinject
Go takes an implementation-first approach:
Do not define interfaces before they are used: without a realistic example of usage, it is too difficult to see whether an interface is even necessary, let alone what methods it ought to contain.
Also:
-
DI can be used to match an implementation to an interface
-
do not create a constructor, that returns an interface - even though wire uses standard Go type identity rules for matching.
-
interface binding should be put into the provider set
Inject struct fields.