implement AddEqual (#10)

deepequal.go

@@ -35,6 +35,11 @@ func (teq Teq) deepValueEqual(
 		return false
 	}
 
+	eq, ok := teq.equals[v1.Type()]
+	if ok {
+		return eq(v1, v2)
+	}
+
 	tr, ok := teq.transforms[v1.Type()]
 	if ok {
 		t1 := tr(v1)

teq.go

@@ -11,6 +11,7 @@ type Teq struct {
 
 	transforms map[reflect.Type]func(reflect.Value) reflect.Value
 	formats    map[reflect.Type]func(reflect.Value) string
+	equals     map[reflect.Type]func(reflect.Value, reflect.Value) bool
 }
 
 // New returns new instance of Teq.
@@ -20,6 +21,7 @@ func New() Teq {
 
 		transforms: make(map[reflect.Type]func(reflect.Value) reflect.Value),
 		formats:    make(map[reflect.Type]func(reflect.Value) string),
+		equals:     make(map[reflect.Type]func(reflect.Value, reflect.Value) bool),
 	}
 }
 
@@ -109,6 +111,34 @@ func (teq *Teq) AddFormat(format any) {
 	teq.formats[ty.In(0)] = reflectFormat
 }
 
+// AddEqual adds an equal function to Teq.
+// The equal function must have two arguments with the same type and one return value of bool.
+// If the passed equal function is not valid, it will panic.
+// The equal function will be used for equality check instead of the default equality check.
+func (teq *Teq) AddEqual(equal any) {
+	ty := reflect.TypeOf(equal)
+	if ty.Kind() != reflect.Func {
+		panic("equal must be a function")
+	}
+	if ty.NumIn() != 2 {
+		panic("equal must have two arguments")
+	}
+	if ty.In(0) != ty.In(1) {
+		panic("equal must have two arguments with the same type")
+	}
+	if ty.NumOut() != 1 {
+		panic("equal must have only one return value")
+	}
+	if ty.Out(0).Kind() != reflect.Bool {
+		panic("equal must return bool")
+	}
+	equalValue := reflect.ValueOf(equal)
+	reflectEqual := func(v1, v2 reflect.Value) bool {
+		return equalValue.Call([]reflect.Value{v1, v2})[0].Bool()
+	}
+	teq.equals[ty.In(0)] = reflectEqual
+}
+
 func (teq Teq) equal(x, y any) bool {
 	if x == nil || y == nil {
 		return x == y

teq_customized_test.go

@@ -1,6 +1,7 @@
 package teq_test
 
 import (
+	"math"
 	"reflect"
 	"testing"
 	"time"
@@ -47,6 +48,43 @@ func TestEqual_Customized(t *testing.T) {
 			t.Error("expected ds1 != ds2, got ds1 == ds2 with reflect.DeepEqual")
 		}
 	})
+
+	t.Run("AddEqual", func(t *testing.T) {
+		t.Run("float64", func(t *testing.T) {
+			d := teq.New()
+			c := teq.New()
+			c.AddEqual(func(a, b float64) bool {
+				const epsilon = 1e-3
+				return math.Abs(a-b) < epsilon
+			})
+
+			d.NotEqual(t, 1.0, 1.001)
+			c.Equal(t, 1.0, 1.001)
+			c.NotEqual(t, 1.0, 1.002)
+
+			d.NotEqual(t, float32(1.0), float32(1.001))
+			c.NotEqual(t, float32(1.0), float32(1.001))
+
+			d.NotEqual(t, []float64{1.0, 1.0, 1.001}, []float64{1.001, 1.0, 1.0})
+			c.Equal(t, []float64{1.0, 1.0, 1.001}, []float64{1.001, 1.0, 1.0})
+		})
+
+		t.Run("time.Time", func(t *testing.T) {
+			d := teq.New()
+			c := teq.New()
+			c.AddEqual(func(a, b time.Time) bool {
+				return a.Equal(b)
+			})
+
+			secondsEastOfUTC := int((8 * time.Hour).Seconds())
+			beijing := time.FixedZone("Beijing Time", secondsEastOfUTC)
+			d1 := time.Date(2000, 2, 1, 12, 30, 0, 0, time.UTC)
+			d2 := time.Date(2000, 2, 1, 20, 30, 0, 0, beijing)
+
+			d.NotEqual(t, d1, d2)
+			c.Equal(t, d1, d2)
+		})
+	})
 }
 
 func TestEqual_CustomizedFormat(t *testing.T) {