goimpl

A tool to generate stub implementation of an interface.

The output is printed to stdout, errors (if any) — to stderr. ##Installation

go get github.com/sasha-s/goimpl/cmd/goimpl

In a nutshell

goimpl io.ReadWriteCloser "*pkg.impl"

Would print

package pkg

type impl struct{}

func (i *impl) Close() (err error) {
    return
}

func (i *impl) Read(u []uint8) (i1 int, err error) {
    return
}

func (i *impl) Write(u []uint8) (i1 int, err error) {
    return
}

Let's say you already have this (the Writer is almost http.ResponseWriter, but not quite):

package w12

import "net/http"

type Writer struct{}

func (w Writer) Write(float64) (error, *int) {
    return nil, nil
}

func (Writer) Header() http.Header {
    return nil
}

Running

goimpl -existing http.ResponseWriter "w12.Writer"

Gives

package w12

type Writer struct{}

// inputs[0]: had `float64` want `[]uint8`; outputs[0]: had `error` want `int`; outputs[1]: had `*int` want `error`
func (w Writer) Write(u []uint8) (i int, err error) {
	return
}

func (w Writer) WriteHeader(i int) {
	return
}

Here only the missing methods and the methods with wrong signature are generates.

Usage

Usage: goimpl [flags] [import1] [import2...] package.interfaceTypeName [(*|&)][package2.]typeName
This would generate empty implementation of the interfaceTypeName.
  -existing=false: Would trigger generation of missing method for the existing type(struct). Note, that if you want to use a pointer receiver prefix the type with '&'.
  -goimports=true: Run goimports on the generated code. The generated code might not compile if this is not set.
  -named=true: Generate named return values. The genrated code might not compile if this is not set.

Alternative(s)

impl

• impl is parsing AST, goimpl is using reflection.
• impl is much faster and has better error reporting.
• goimpl generates complete code that (usually) compiles (package/ imports).
• goimpl can generate a minimum update for the exising implementation.
• goimpl can work with ambiguous package names.