Function: AcceptIf (#198)

AcceptIf returns another function of the same signature as the apply function but also includes a bool value to indicate success or failure.
A predicate function that takes an argument of type T and returns a bool.
An apply function that also takes an argument of type T and returns a modified value of the same type.

function/function.go

@@ -136,6 +136,27 @@ func Pipeline[T any](funcs ...func(T) T) func(T) T {
 	}
 }
 
+// AcceptIf returns another function of the same signature as the apply function but also includes a bool value to indicate success or failure.
+// A predicate function that takes an argument of type T and returns a bool.
+// An apply function that also takes an argument of type T and returns a modified value of the same type.
+func AcceptIf[T any](predicate func(T) bool, apply func(T) T) func(T) (T, bool) {
+	if predicate == nil {
+		panic("programming error: predicate must be not nil")
+	}
+
+	if apply == nil {
+		panic("programming error: apply must be not nil")
+	}
+
+	return func(t T) (T, bool) {
+		if !predicate(t) {
+			var defaultValue T
+			return defaultValue, false
+		}
+		return apply(t), true
+	}
+}
+
 func unsafeInvokeFunc(fn any, args ...any) []reflect.Value {
 	fv := reflect.ValueOf(fn)
 	params := make([]reflect.Value, len(args))

function/function_example_test.go

@@ -145,3 +145,32 @@ func ExamplePipeline() {
 	// Output:
 	// 36
 }
+
+func ExampleAcceptIf() {
+
+	adder := AcceptIf(
+		And(
+			func(x int) bool {
+				return x > 10
+			}, func(x int) bool {
+				return x%2 == 0
+			}),
+		func(x int) int {
+			return x + 1
+		},
+	)
+
+	result, ok := adder(20)
+	fmt.Println(result)
+	fmt.Println(ok)
+
+	result, ok = adder(21)
+	fmt.Println(result)
+	fmt.Println(ok)
+
+	// Output:
+	// 21
+	// true
+	// 0
+	// false
+}

function/function_test.go

@@ -162,3 +162,63 @@ func TestPipeline(t *testing.T) {
 
 	assert.Equal(36, f(2))
 }
+
+func TestAcceptIf(t *testing.T) {
+	assert := internal.NewAssert(t, "AcceptIf")
+
+	adder := AcceptIf(
+		And(
+			func(x int) bool {
+				return x > 10
+			}, func(x int) bool {
+				return x%2 == 0
+			}),
+		func(x int) int {
+			return x + 1
+		},
+	)
+
+	result, ok := adder(20)
+	assert.Equal(21, result)
+	assert.Equal(true, ok)
+
+	result, ok = adder(21)
+	assert.Equal(0, result)
+	assert.Equal(false, ok)
+}
+
+func TestAcceptIfPanicMissingPredicate(t *testing.T) {
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestAcceptIfPanicMissingPredicate")
+
+	defer func() {
+		v := recover()
+		assert.Equal("programming error: predicate must be not nil", v)
+	}()
+
+	AcceptIf(
+		nil,
+		func(x int) int {
+			return x
+		},
+	)
+}
+
+func TestAcceptIfPanicMissingApply(t *testing.T) {
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestAcceptIfPanicMissingApply")
+
+	defer func() {
+		v := recover()
+		assert.Equal("programming error: apply must be not nil", v)
+	}()
+
+	AcceptIf(
+		func(i int) bool {
+			return false
+		},
+		nil,
+	)
+}