Add Contains filter

it/filter/filter.go

@@ -2,8 +2,10 @@
 package filter
 
 import (
+	"bytes"
 	"cmp"
 	"regexp"
+	"strings"
 )
 
 // IsEven returns true when the provided integer is even.
@@ -106,3 +108,14 @@ func Match[T string | []byte](pattern *regexp.Regexp) func(T) bool {
 		return pattern.MatchString(string(term))
 	}
 }
+
+// Contains returns a function that returns true when the provided string or
+// byte slice is found within another string or byte slice. See
+// [strings.Contains] and [bytes.Contains].
+func Contains[T string | []byte](t T) func(T) bool {
+	if s, ok := any(t).(string); ok {
+		return func(v T) bool { return strings.Contains(any(v).(string), s) }
+	}
+
+	return func(v T) bool { return bytes.Contains(any(v).([]byte), any(t).([]byte)) }
+}

it/filter/filter_test.go

@@ -154,3 +154,23 @@ func ExampleMatch_bytes() {
 
 	// Output: foobar
 }
+
+func ExampleContains_string() {
+	strings := slices.Values([]string{"foobar", "barfoo"})
+
+	for element := range it.Filter(strings, filter.Contains("rfoo")) {
+		fmt.Println(element)
+	}
+
+	// Output: barfoo
+}
+
+func ExampleContains_bytes() {
+	strings := slices.Values([][]byte{[]byte("foobar"), []byte("barfoo")})
+
+	for element := range it.Filter(strings, filter.Contains([]byte("rfoo"))) {
+		fmt.Println(string(element))
+	}
+
+	// Output: barfoo
+}