From a8777fa1caccb3ffea5799d7a53c8f374941e78a Mon Sep 17 00:00:00 2001
From: b97tsk <b97tsk@gmail.com>
Date: Thu, 25 Jan 2024 14:44:34 +0800
Subject: [PATCH] Add method IsValid to type Interval

---
 intervalset.go      |  8 ++++++++
 intervalset_test.go | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/intervalset.go b/intervalset.go
index 5b29f46..93b76a6 100644
--- a/intervalset.go
+++ b/intervalset.go
@@ -44,6 +44,14 @@ func (r Interval[E]) Equal(r2 Interval[E]) bool {
 	return r.Low.Compare(r2.Low) == 0 && r.High.Compare(r2.High) == 0
 }
 
+// IsValid reports whether r is a valid Interval.
+// A valid Interval r either satisfies r.Low.Compare(r.High) < 0 or equals to
+// the zero value.
+func (r Interval[E]) IsValid() bool {
+	c := r.Low.Compare(r.High)
+	return c < 0 || c == 0 && r.Equal(Interval[E]{})
+}
+
 // Set returns the set of elements that are in r.
 // If r is the zero value, Set returns an empty set.
 // If r is an invalid Interval, Set panics.
diff --git a/intervalset_test.go b/intervalset_test.go
index 96075d3..f3b1976 100644
--- a/intervalset_test.go
+++ b/intervalset_test.go
@@ -7,6 +7,25 @@ import (
 	"github.com/b97tsk/intervals/elems"
 )
 
+func TestIsValid(t *testing.T) {
+	type E = elems.Int
+
+	assertions := []bool{
+		Interval[E]{}.IsValid(),
+		One[E](0).IsValid(),
+		Range[E](1, 5).IsValid(),
+		!Range[E](5, 1).IsValid(),
+		!Range[E](5, 5).IsValid(),
+	}
+
+	for i, ok := range assertions {
+		if !ok {
+			t.Fail()
+			t.Logf("Case %v: FAILED", i)
+		}
+	}
+}
+
 func TestCreation(t *testing.T) {
 	type E = elems.Int