gogen

AST rewrite powered generics for Go

Usage

Somewhere in your code you need to define one or more generic types. Something like:

type I interface{}
type F interface{}

From here, you can write any code that uses those generic type (including tests):

func Add(left, right I) I {
    return left + right
}
func Sub(left, right F) F {
    return left - right
}

Using the gogen CLI you can then render the generic code with concrete types:

gogen -source github.com/username/package -destination . -rewrite "I=uint16" -rewrite "F=float64

The source code will be rewritten without the type I interface{} lines and with all references to generic types replaced with concrete types.

func Add(left, right uint16) uint16 {
    return left + right
}
func Sub(left, right float64) float64 {
    return left - right
}

The output will be formatted with gofmt (but not goimports).

More Options

In addition to direct rewrites, the CLI also offers the following options:

• -unstar T

  This option triggers the rewrite of *T within the source to T before being rewritten as the concrete type. This is useful if rendering a generic as an interface type (such as `-rewrite "T=io.Reader"). The option may be given multiple times to unstar multiple generic types.

• -rewrite "T=*int"

  If the concrete type given in a rewrite rule is prefixed with an * then a pointer type will be used. If the generic type is already a pointer then this could result in a double pointer to the concrete type. Use the unstar flag to prevent this. Any number of rewrites may be given per invocation.

• -rewrite "T=pkg.Name"

  If the concrete type has a package prefix then the resulting code will correctly select the type from the target package. However, the rewrite will not change import statements or add new ones. It is recommended to use something like goimports to correct any missing or excess import statements after rewrites.

• -package newname

  The package option causes the renderer to set a custom package name in all files rendered. By default, the original package name is reused.

License

This project is available under the Apache2.0 license. See the LICENSE file in this repository for the complete license text.