ImplGen

ImoGen is a interface implementation code generation tool for the Go programming language.

Installation

Once you have installed Go, install the implgen tool.

To get the latest released version use:

GO111MODULE=on go get github.com/ssoor/implgen@latest

If you use implgen in your CI pipeline, it may be more appropriate to fixate on a specific implgen version.

Building Implemented Code

input code:

// Doc:Test Foo
type Foo interface {
  // Doc:Foo.Bar
  Bar(x int) int // Comment:Foo.Bar
}

output code:

// Doc:Test Foo
type Foo struct {
}

// Doc:Test Foo
func NewFoo() *Foo {
    implObj := &Foo{}

    // TODO: NewFoo() Not implemented

    return implObj
}

// Doc:Foo.Bar
func (m *Foo) Bar(x int) int {  // Comment:Foo.Bar
    // TODO: Foo.Bar(x int) int Not implemented

    panic("Foo.Bar(x int) int Not implemented")
}

Running implgen

implgen has two modes of operation: source and reflect. Source mode generates mock interfaces from a source file. It is enabled by using the -source flag. Other flags that may be useful in this mode are -imports and -aux_files.

Example:

implgen -source=foo.go [other options]

Reflect mode generates mock interfaces by building a program that uses reflection to understand interfaces. It is enabled by passing two non-flag arguments: an import path, and a comma-separated list of symbols.

You can use "." to refer to the current path's package.

Example:

implgen database/sql/driver Conn,Driver

# Convenient for `go:generate`.
implgen . Conn,Driver

The implgen command is used to generate source code for a implement class given a Go source file containing interfaces to be implemented. It supports the following flags:

• -source: A file containing interfaces to be implemented.

• -destination: A file to which to write the resulting source code. If you don't set this, the code is printed to standard output.

• -package: The package to use for the resulting implement class source code. If you don't set this, the package name is impl_ concatenated with the package of the input file.

• -impl_names: A list of custom names for generated implements. This is specified as a comma-separated list of elements of the form Repository=MockSensorRepository,Endpoint=MockSensorEndpoint, where Repository is the interface name and MockSensorRepository is the desired implement name (implement factory method and implement recorder will be named after the implement). If one of the interfaces has no custom name specified, then default naming convention will be used.

• -self_package: The full package import path for the generated code. The purpose of this flag is to prevent import cycles in the generated code by trying to include its own package. This can happen if the implement's package is set to one of its inputs (usually the main one) and the output is stdio so implgen cannot detect the final output package. Setting this flag will then tell implgen which import to exclude.

• -copyright_file: Copyright file used to add copyright header to the resulting source code.

• -imports: A list of explicit imports that should be used in the resulting source code, specified as a comma-separated list of elements of the form foo=bar/baz, where bar/baz is the package being imported and foo is the identifier to use for the package in the generated source code.

• -aux_files: A list of additional files that should be consulted to resolve e.g. embedded interfaces defined in a different file. This is specified as a comma-separated list of elements of the form foo=bar/baz.go, where bar/baz.go is the source file and foo is the package name of that file used by the -source file.

• -build_flags: (reflect mode only) Flags passed verbatim to go build.

For an example of the use of implgen, see the sample/ directory. In simple cases, you will need only the -source flag.