Accept Interfaces, Return Concrete Types

You can get ireturn with go install command. Go1.18+ required.

go install github.com/butuzov/ireturn/cmd/ireturn@latest

Or you can download the suitable binary from the releases section.

ireturn work with two arguments (but allow to use of only one of them in the same moment):

• accept - accept-list of the comma-separated interfaces.
• reject - reject-list of the comma-separated interfaces.

By default, ireturn will accept all errors (error), empty interfaces (interfaces{}), anonymous interfaces declarations ( interface { methodName() } ), interfaces from standard library, and generic interfaces (introduced in go1.18) as a valid ones.

Interfaces in the list can be provided as regexps or keywords ("error" for "error", "empty" for interface{}, anon for anonymous interfaces):

# allow usage of empty interfaces, errors and Doer interface from any package.
ireturn --accept="\\.Doer,error,empty" ./...
# reject standard library interfaces and plinko.Payload as valid ones
ireturn --reject="std,github.com/shipt/plinko.Payload" ./...
# default settings allows errors, empty interfaces, anonymous declarations and standard library
ireturn ./...
# checkfor non idiomatic interface names
ireturn -allow="error,generic,anon,stdlib,.*(or|er)$" ./...

You can use shorthand for some types of interfaces:

• empty for interface{} type
• anon for anonymous declarations interface{ someMethod() }
• error for error type
• stdlib for all interfaces from standard library.
• generic for generic interfaces (added in go1.18)

golangci-lint compliant disable directive //nolint: ireturn can be used with ireturn

- uses: butuzov/ireturn-linter@main
  with:
    allow: "error,empty"

// Bad.
type Doer interface { Do() }
type IDoer struct{}
func New() Doer { return new(IDoer)}
func (d *IDoer) Do() {/*...*/}

// Good.
type Doer interface { Do() }
type IDoer struct{}
func New() *IDoer { return new(IDoer)}
func (d *IDoer) Do() {/*...*/}

// Very Good (Verify Interface Compliance in compile time)
var _ Doer = (*IDoer)(nil)

type Doer interface { Do() }
type IDoer struct{}
func New() *IDoer { return new(IDoer)}
func (d *IDoer) Do() {/*...*/}

• Rob Pike's comment on "Accept Interfaces Return Struct in Go"
• Accept Interfaces Return Struct in Go
• Accept Interface Return Struct
• What “accept interfaces, return structs” means in Go