add filter function (#6)

Author: mikehelmick

slice/filter.go

@@ -0,0 +1,27 @@
+// Copyright 2023 the go-functional authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package slice
+
+// Filter returns a new slice of only the elements in the list
+// that match the provided matchFn.
+func Filter[T any](in []T, matchFn MatchFn[T]) []T {
+	rtn := make([]T, 0, len(in))
+	for _, e := range in {
+		if matchFn(e) {
+			rtn = append(rtn, e)
+		}
+	}
+	return rtn
+}

slice/filter_test.go

@@ -0,0 +1,71 @@
+// Copyright 2023 the go-functional authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package slice_test
+
+import (
+	"fmt"
+
+	"github.com/mikehelmick/go-functional/slice"
+)
+
+func ExampleFilter() {
+	type Account struct {
+		Name   string
+		Writer bool
+	}
+
+	input := []*Account{
+		{
+			Name:   "Bob",
+			Writer: false,
+		},
+		{
+			Name:   "Alice",
+			Writer: true,
+		},
+		{
+			Name:   "Steve",
+			Writer: false,
+		},
+	}
+
+	// Function to check if an element is even
+	isWriter := func(x *Account) bool {
+		return x.Writer
+	}
+
+	writers := slice.Filter(input, isWriter)
+	fmt.Printf("Writers:\n")
+	for _, writer := range writers {
+		fmt.Printf(" - name: %v\n", writer.Name)
+	}
+
+	isReadOnly := func(x *Account) bool {
+		return !x.Writer
+	}
+
+	readers := slice.Filter(input, isReadOnly)
+	fmt.Printf("Readers:\n")
+	for _, reader := range readers {
+		fmt.Printf(" - name: %v\n", reader.Name)
+	}
+
+	// Output:
+	// Writers:
+	//  - name: Alice
+	// Readers:
+	//  - name: Bob
+	//  - name: Steve
+}