ptr.go

package ptr

import (
	"github.com/go-board/std/cmp"
)

func zero[T any]() (v T) { return }

// Ref return reference of value
func Ref[T any](t T) *T { return &t }

// RefOrNil return reference of value if it not the zero value, else return nil
func RefOrNil[T comparable](t T) *T {
	if t == zero[T]() {
		return nil
	}
	return &t
}

// ValueOr return value of pointer if not nil, else return default value.
func ValueOr[T any](v *T, d T) T {
	if v == nil {
		return d
	}
	return *v
}

// ValueOrZero return value of pointer if not nil, else return zero value.
func ValueOrZero[T any](v *T) T {
	return ValueOr(v, zero[T]())
}

func OrZero[T any](v *T) *T {
	if v == nil {
		return Ref(zero[T]())
	}
	return v
}

// Compare compares two pointer. If both non-nil, compare underlying data,
// if both nil, return 0, non-nil pointer is always greater than nil pointer.
func Compare[T cmp.Ordered](l, r *T) int {
	return CompareBy(l, r, cmp.Compare[T])
}

func CompareBy[T any](l, r *T, cmp func(T, T) int) int {
	if l != nil && r != nil {
		return cmp(*l, *r)
	}
	if l == nil && r == nil {
		return 0
	}
	if l != nil {
		return +1
	}
	return -1
}

// Equal test whether two pointer are equal. If both non-nil, test underlying data,
// if both nil, return true, else return false
func Equal[T comparable](l, r *T) bool {
	return EqualBy(l, r, cmp.Equal[T])
}

func EqualBy[T any](l, r *T, eq func(T, T) bool) bool {
	if l != nil && r != nil {
		return eq(*l, *r)
	} else if l == nil && r == nil {
		return true
	}
	return false
}