Add ParseStringerEnumv0.6.0

2 files changed, 46 insertions, 0 deletions

diff --git a/flag.go b/flag.go
index f9d048e..96c74d2 100644
--- a/flag.go
+++ b/flag.go
@@ -184,6 +184,20 @@ func ParseStringEnum(values ...string) ParseFunc[string] {
 	}
 }
 
+// ParseStringerEnum returns a ParseFunc that will return the first
+// value having a string value matching the string passed.
+func ParseStringerEnum[T fmt.Stringer](values ...T) ParseFunc[T] {
+	return func(s string) (T, error) {
+		for _, val := range values {
+			if s == val.String() {
+				return val, nil
+			}
+		}
+		var zero T
+		return zero, UnknownEnumValueError[T]{s, values}
+	}
+}
+
 // ParseTime parses a string according to the time.RFC3339 format.
 func ParseTime(s string) (time.Time, error) {
 	return time.Parse(time.RFC3339, s)
diff --git a/flag_test.go b/flag_test.go
index 3273775..411174a 100644
--- a/flag_test.go
+++ b/flag_test.go
@@ -203,3 +203,35 @@ func TestParseStringEnum(s *testing.T) {
 		t.AssertEqual("", val)
 	})
 }
+
+func TestParseStringerEnum(s *testing.T) {
+	t := &core.T{T: s, Options: cmp.Options{fakeEnumComparer}}
+	parser := core.ParseStringerEnum(fakeEnumFoo, fakeEnumBar)
+
+	t.Run("Match", func(t *core.T) {
+		val, err := parser("FOO")
+		t.AssertErrorIs(nil, err)
+		t.AssertEqual(fakeEnumFoo, val)
+	})
+
+	t.Run("UnknownValue", func(t *core.T) {
+		val, err := parser("baz")
+		var exp core.UnknownEnumValueError[fakeEnum]
+		if t.AssertErrorAs(&exp, err) {
+			t.AssertEqual("baz", exp.Actual)
+			t.AssertEqual([]fakeEnum{fakeEnumFoo, fakeEnumBar}, exp.Expected)
+		}
+		t.AssertEqual(fakeEnum{}, val)
+	})
+}
+
+type fakeEnum struct{ string }
+
+var (
+	fakeEnumFoo = fakeEnum{"FOO"}
+	fakeEnumBar = fakeEnum{"BAR"}
+
+	fakeEnumComparer = cmp.Comparer(func(x, y fakeEnum) bool { return x == y })
+)
+
+func (e fakeEnum) String() string { return e.string }