Check exhaustiveness of switch statements against discriminated unions.
go install github.com/thematthopkins/discriminatedunion/cmd/discriminatedunion@latest
Go frequently uses interfaces to signify discriminated unions. One bit that is lacking though is it does not have a way of enforcing that switches exhaustively handle all members of a discriminated union. This analyzer performs that check, so that if you add a new member to a discriminated union, you can have confidence that all type switches will be forced to account for the new member.
Given a discriminated union defined by:
package shape
type Circle struct {
float32 Radius
}
type Square struct {
float32 Width
}
type Arc struct {
float32 Radius
float32 Radians
}
type Shape interface {
// IsShape takes the form Is<interface>, which tells the discriminatedunion
// checker that it is a discriminated union.
IsShape()
}
// The receivers below signify which structs are members of the Shape discriminated union
func (Circle) IsShape() {}
func (Square) IsShape() {}
func (Arc) IsShape() {}with the code below:
package shapeprinter
import (
"fmt"
"shape"
)
func printShape(s shape.Shape) {
switch s := s {
case shape.Circle:
fmt.Printf("Circle Radius %v\n", s.Radius)
case shape.Square:
fmt.Printf("Square Width %v\n", s.Width)
}
}running discriminatedunion ./..., or adding it to your go/analysis/multichecker will print:
shapeprinter.go:14:3: missing cases for discriminated union types: shape.Arc