Pre-declare global type variables (#302)

Co-authored-by: Damien Neil <neild@users.noreply.github.com>

Author: dsnet

cmp/compare.go

@@ -144,7 +144,7 @@ func rootStep(x, y interface{}) PathStep {
 	// so that they have the same parent type.
 	var t reflect.Type
 	if !vx.IsValid() || !vy.IsValid() || vx.Type() != vy.Type() {
-		t = reflect.TypeOf((*interface{})(nil)).Elem()
+		t = anyType
 		if vx.IsValid() {
 			vvx := reflect.New(t).Elem()
 			vvx.Set(vx)

cmp/report_compare.go

@@ -115,7 +115,7 @@ func (opts formatOptions) FormatDiff(v *valueNode, ptrs *pointerReferences) (out
 
 	// For leaf nodes, format the value based on the reflect.Values alone.
 	// As a special case, treat equal []byte as a leaf nodes.
-	isBytes := v.Type.Kind() == reflect.Slice && v.Type.Elem() == reflect.TypeOf(byte(0))
+	isBytes := v.Type.Kind() == reflect.Slice && v.Type.Elem() == byteType
 	isEqualBytes := isBytes && v.NumDiff+v.NumIgnored+v.NumTransformed == 0
 	if v.MaxDepth == 0 || isEqualBytes {
 		switch opts.DiffMode {

cmp/report_reflect.go

@@ -16,6 +16,13 @@ import (
 	"github.com/google/go-cmp/cmp/internal/value"
 )
 
+var (
+	anyType    = reflect.TypeOf((*interface{})(nil)).Elem()
+	stringType = reflect.TypeOf((*string)(nil)).Elem()
+	bytesType  = reflect.TypeOf((*[]byte)(nil)).Elem()
+	byteType   = reflect.TypeOf((*byte)(nil)).Elem()
+)
+
 type formatValueOptions struct {
 	// AvoidStringer controls whether to avoid calling custom stringer
 	// methods like error.Error or fmt.Stringer.String.
@@ -205,7 +212,7 @@ func (opts formatOptions) FormatValue(v reflect.Value, parentKind reflect.Kind,
 		}
 
 		// Check whether this is a []byte of text data.
-		if t.Elem() == reflect.TypeOf(byte(0)) {
+		if t.Elem() == byteType {
 			b := v.Bytes()
 			isPrintSpace := func(r rune) bool { return unicode.IsPrint(r) || unicode.IsSpace(r) }
 			if len(b) > 0 && utf8.Valid(b) && len(bytes.TrimFunc(b, isPrintSpace)) == 0 {

cmp/report_slices.go

@@ -104,7 +104,7 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
 	case t.Kind() == reflect.String:
 		sx, sy = vx.String(), vy.String()
 		isString = true
-	case t.Kind() == reflect.Slice && t.Elem() == reflect.TypeOf(byte(0)):
+	case t.Kind() == reflect.Slice && t.Elem() == byteType:
 		sx, sy = string(vx.Bytes()), string(vy.Bytes())
 		isString = true
 	case t.Kind() == reflect.Array:
@@ -232,7 +232,7 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
 			var out textNode = &textWrap{Prefix: "(", Value: list2, Suffix: ")"}
 			switch t.Kind() {
 			case reflect.String:
-				if t != reflect.TypeOf(string("")) {
+				if t != stringType {
 					out = opts.FormatType(t, out)
 				}
 			case reflect.Slice:
@@ -327,12 +327,12 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
 	switch t.Kind() {
 	case reflect.String:
 		out = &textWrap{Prefix: "strings.Join(", Value: out, Suffix: fmt.Sprintf(", %q)", delim)}
-		if t != reflect.TypeOf(string("")) {
+		if t != stringType {
 			out = opts.FormatType(t, out)
 		}
 	case reflect.Slice:
 		out = &textWrap{Prefix: "bytes.Join(", Value: out, Suffix: fmt.Sprintf(", %q)", delim)}
-		if t != reflect.TypeOf([]byte(nil)) {
+		if t != bytesType {
 			out = opts.FormatType(t, out)
 		}
 	}