Initial commit

sortable.go

@@ -0,0 +1,42 @@
+package stl
+
+// ImplicitSortable are types that can be compared with
+// the less operator <, among others.
+//
+// As with C++, two keys are considered equal if neither
+// x < y nor y < x, so these interfaces have nothing to
+// do with Go's 'comparable' whatsoever.
+//
+// This behavior can be overridden by defining another
+// type and then add a Compare method to the original key.
+type ImplicitSortable interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr | ~string | ~float32 | ~float64
+}
+
+// Sorter is a interface used in the construction of
+// many collection types, to compare two keys with
+// the '<' operator by default.
+type Sorter[T any] interface {
+	Compare(x, y T) bool
+}
+
+// Less implements Sorter for ImplicitSortables using the '<' operator.
+type Less[T ImplicitSortable] struct{}
+
+func (Less[T]) Compare(x, y T) bool {
+	return x < y
+}
+
+// Greater implements Sorter for ImplicitSortables using the '>' operator.
+type Greater[T ImplicitSortable] struct{}
+
+func (Greater[T]) Compare(x, y T) bool {
+	return x > y
+}
+
+// Equal determines if the two keys are considered equal,
+// i.e., neither x < y nor y < x, per C++ traditions.
+func Equal[C Sorter[T], T any](x, y T) bool {
+	var c C
+	return !c.Compare(x, y) && !c.Compare(y, x)
+}