Function Comparer

cmp/options.go:355–365

Comparer returns an [Option] that determines whether two values are equal to each other. The comparer f must be a function "func(T, T) bool" and is implicitly filtered to input values assignable to T. If T is an interface, it is possible that f is called with two values of different concrete types

(f interface{})

//   - Deterministic: equal(x, y) == equal(x, y)
//   - Pure: equal(x, y) does not modify x or y
func Comparer(f interface{}) Option {
	v := reflect.ValueOf(f)
	if !function.IsType(v.Type(), function.Equal) || v.IsNil() {
		panic(fmt.Sprintf("invalid comparer function: %T", f))
	}
	cm := &comparer{fnc: v}
	if ti := v.Type().In(0); ti.Kind() != reflect.Interface || ti.NumMethod() > 0 {
		cm.typ = ti
	}
	return cm
}

type comparer struct {
	core