go-oneof

This tool is aimed to generate a Go code to partially replicate lacking discriminated unions functionality in Go

Installation

GO111MODULE=on go get github.com/sirkon/go-oneof

How to use it

Need to write a special structure with name staring from oneof (there are further limitations, but they will be reported by the utility itself). Like this:

// node.go file

package node

//go:generate go-oneof node.go

type oneofNode struct {
    Value string
    OperatorSum struct {
        Left  *oneofNode
        Right *oneofNode
    }
}

And run go generate over it

The result will be

package node

//go:generate go-oneof node.go

type oneofNode struct {
	Value       string
	OperatorSum struct {
		Left  *oneofNode
		Right *oneofNode
	}
}

// Node an interface to limit available implementations to emulate discriminated union type
type Node interface {
	isNode()
}

// Value branch of Node
type Value string

func (Value) isNode() {}

// OperatorSum branch of Node
type OperatorSum struct {
	Left  Node
	Right Node
}

func (OperatorSum) isNode() {}

Some notes:

• type oneofName will generate interface Name with private method isName

• each field causes an implementation of generated Name

• comments existed in the source file will disappear in its replacement

• free comments will stay, but will be moved on the top of the file

• You may use --pointer or -p call parameter to implement Name of source struct fields over pointer to these structs, not structs themselves, i.e. Node implementation for OperatorSum would be

  func (*OperatorSum) isNode()
  

  in this example

• This source file may have errors like reference to entities that do not exists. This may work for self reference, but the usage of *oneofNode (change to actual name) is preferable.