Add util package

internal/util/util.go

@@ -0,0 +1,101 @@
+package util
+
+import "image/color"
+
+// IndexOf returns the index of needle within haystack. If needle does not exist
+// within haystack, it returns -1.
+func IndexOf[T comparable] (haystack []T, needle T) int {
+	for index, test := range haystack {
+		if test == needle {
+			return index
+		}
+	}
+	return -1
+}
+
+// Remove removes an element from slice at index.
+func Remove[T any] (slice []T, index int) []T {
+	return append(slice[:index], slice[index + 1:]...)
+}
+
+// Insert inserts an element into slice at index.
+func Insert[T any] (slice []T, index int, element T) []T {
+	slice = append(slice[:index + 1], slice[index:]...)
+	slice[index] = element
+	return slice
+}
+
+// Transparent returns whether or not a color has transparency.
+func Transparent (c color.Color) bool {
+	_, _, _, a := c.RGBA()
+	return a != 0xFFFF
+}
+
+// Set is a set of unique items, built on top of map.
+type Set[T comparable] map[T] struct { }
+
+// Empty returns true if there are no items in the set.
+func (set Set[T]) Empty () bool {
+	return set == nil || len(set) == 0
+}
+
+// Has returns true if the set contains item.
+func (set Set[T]) Has (item T) bool {
+	if set == nil {
+		return false
+	}
+	_, ok := set[item]
+	return ok
+}
+
+// Add adds an item to the set.
+func (set Set[T]) Add (item T) {
+	set[item] = struct { } { }
+}
+
+// Pop removes the first accessible item from the set and returns it.
+func (set Set[T]) Pop () (item T) {
+	for item := range set {
+		delete(set, item)
+		return item
+	}
+	return
+}
+
+// Memo holds a cached value.
+type Memo[T any] struct {
+	cache  T
+	valid  bool
+	update func () T
+}
+
+// NewMemo creates a new Memo which will take its value from the specified
+// update callback.
+func NewMemo[T any] (update func () T) Memo[T] {
+	return Memo[T] {
+		update: update,
+	}
+}
+
+// Value returns the Memo's value, updating it if the current cached value is
+// invalid.
+func (this *Memo[T]) Value () T {
+	if !this.valid {
+		this.cache = this.update()
+	}
+	return this.cache
+}
+
+// Invalidate marks the Memo's value as invalid, which will cause it to be
+// updated the next time Value is called.
+func (this *Memo[T]) Invalidate () {
+	this.valid = false
+}
+
+// InvalidateTo invalidates the Memo and sets its value. The new value will be
+// entirely inaccessible. This is only intended to be used for setting a
+// reference to nil
+func (this *Memo[T]) InvalidateTo (value T) {
+	this.Invalidate()
+	this.cache = value
+}