impl

A library and a command line that intelligently implements Go interfaces for any given type.

Features:

• Go Modules aware
• Only adds the missing methods
• Reports an error if a method with a conflicting type signature already exists
• Adds "import" declarations to the file if any of the interface methods require it
• Recursively implement methods in embedded interfaces
• Adjusts the method function signature based on imports, such as replacing *models.Person with *Person if the target is in the "models" package already.
• Understands "." imports as well as "_" named imports

Install

As a command line tool:

go get marwan.io/impl/cmd/impl

As a library:

go get marwan.io/impl

Usage (command line)

Given a type MyType struct {} definition in github.com/my/pkg, you can run the following command:

impl -iface=io.Writer -impl=github.com/my/pkg.MyType

And whichever file MyType is defined in will have func (*MyType) Write(p []byte) (int, error) { panic("unimplemented) }

Similar to gofmt, results will be printed to stdout by default. If you'd like to persist the file instead, then pass the -w flag.

For other options such as json output for tooling, see impl --help.

Usage (library)

import "marwan.io/impl"

resp, err := impl.Implement("io", "Writer", "github.com/my/pkg", "MyType")
// resp.File is the file where MyType was defined
// resp.FileContent is the new content of the entire file that has the Writer method
// resp.Methods is the Go code of all the newly add methods
// resp.AddedImports denotes all new import statements to the concrete type file
// resp.AllImports denotes all import paths of that same file.
// err must be handled

List Available Interfaces

The library can list available interfaces given any import path

impl list -json
["mypkg.MyInterface", "io.Writer", "io.Closer"] # etc

impl list io -json
# ...