reflect: revise for go1.12

related issues: golang/go#23734, golang/go#11104

Update #3

Author: changkun

gosrc/reflect/type.go

@@ -394,16 +394,13 @@ type interfaceType struct {
 // mapType represents a map type.
 type mapType struct {
 	rtype
-	key           *rtype // map key type
-	elem          *rtype // map element (value) type
-	bucket        *rtype // internal bucket structure
-	keysize       uint8  // size of key slot
-	indirectkey   uint8  // store ptr to key instead of key itself
-	valuesize     uint8  // size of value slot
-	indirectvalue uint8  // store ptr to value instead of value itself
-	bucketsize    uint16 // size of bucket
-	reflexivekey  bool   // true if k==k for all keys
-	needkeyupdate bool   // true if we need to update key on an overwrite
+	key        *rtype // map key type
+	elem       *rtype // map element (value) type
+	bucket     *rtype // internal bucket structure
+	keysize    uint8  // size of key slot
+	valuesize  uint8  // size of value slot
+	bucketsize uint16 // size of bucket
+	flags      uint32
 }
 
 // ptrType represents a pointer type.
@@ -593,6 +590,7 @@ const (
 	kindMask        = (1 << 5) - 1
 )
 
+// String returns the name of k.
 func (k Kind) String() string {
 	if int(k) < len(kindNames) {
 		return kindNames[k]
@@ -1858,6 +1856,8 @@ func MapOf(key, elem Type) Type {
 	}
 
 	// Make a map type.
+	// Note: flag values must match those used in the TMAP case
+	// in ../cmd/compile/internal/gc/reflect.go:dtypesym.
 	var imap interface{} = (map[unsafe.Pointer]unsafe.Pointer)(nil)
 	mt := **(**mapType)(unsafe.Pointer(&imap))
 	mt.str = resolveReflectName(newName(s, "", false))
@@ -1866,29 +1866,37 @@ func MapOf(key, elem Type) Type {
 	mt.key = ktyp
 	mt.elem = etyp
 	mt.bucket = bucketOf(ktyp, etyp)
+	mt.flags = 0
 	if ktyp.size > maxKeySize {
 		mt.keysize = uint8(ptrSize)
-		mt.indirectkey = 1
+		mt.flags |= 1 // indirect key
 	} else {
 		mt.keysize = uint8(ktyp.size)
-		mt.indirectkey = 0
 	}
 	if etyp.size > maxValSize {
 		mt.valuesize = uint8(ptrSize)
-		mt.indirectvalue = 1
+		mt.flags |= 2 // indirect value
 	} else {
 		mt.valuesize = uint8(etyp.size)
-		mt.indirectvalue = 0
 	}
 	mt.bucketsize = uint16(mt.bucket.size)
-	mt.reflexivekey = isReflexive(ktyp)
-	mt.needkeyupdate = needKeyUpdate(ktyp)
+	if isReflexive(ktyp) {
+		mt.flags |= 4
+	}
+	if needKeyUpdate(ktyp) {
+		mt.flags |= 8
+	}
+	if hashMightPanic(ktyp) {
+		mt.flags |= 16
+	}
 	mt.ptrToThis = 0
 
 	ti, _ := lookupCache.LoadOrStore(ckey, &mt.rtype)
 	return ti.(Type)
 }
 
+// TODO(crawshaw): as these funcTypeFixedN structs have no methods,
+// they could be defined at runtime using the StructOf function.
 type funcTypeFixed4 struct {
 	funcType
 	args [4]*rtype
@@ -2119,6 +2127,27 @@ func needKeyUpdate(t *rtype) bool {
 	}
 }
 
+// hashMightPanic reports whether the hash of a map key of type t might panic.
+func hashMightPanic(t *rtype) bool {
+	switch t.Kind() {
+	case Interface:
+		return true
+	case Array:
+		tt := (*arrayType)(unsafe.Pointer(t))
+		return hashMightPanic(tt.elem)
+	case Struct:
+		tt := (*structType)(unsafe.Pointer(t))
+		for _, f := range tt.fields {
+			if hashMightPanic(f.typ) {
+				return true
+			}
+		}
+		return false
+	default:
+		return false
+	}
+}
+
 // Make sure these routines stay in sync with ../../runtime/map.go!
 // These types exist only for GC, so we only fill out GC relevant info.
 // Currently, that's just size and the GC program. We also fill in string
@@ -2278,43 +2307,7 @@ type structTypeUncommon struct {
 	u uncommonType
 }
 
-// A *rtype representing a struct is followed directly in memory by an
-// array of method objects representing the methods attached to the
-// struct. To get the same layout for a run time generated type, we
-// need an array directly following the uncommonType memory. The types
-// structTypeFixed4, ...structTypeFixedN are used to do this.
-//
-// A similar strategy is used for funcTypeFixed4, ...funcTypeFixedN.
-
-// TODO(crawshaw): as these structTypeFixedN and funcTypeFixedN structs
-// have no methods, they could be defined at runtime using the StructOf
-// function.
-
-type structTypeFixed4 struct {
-	structType
-	u uncommonType
-	m [4]method
-}
-
-type structTypeFixed8 struct {
-	structType
-	u uncommonType
-	m [8]method
-}
-
-type structTypeFixed16 struct {
-	structType
-	u uncommonType
-	m [16]method
-}
-
-type structTypeFixed32 struct {
-	structType
-	u uncommonType
-	m [32]method
-}
-
-// isLetter returns true if a given 'rune' is classified as a Letter.
+// isLetter reports whether a given 'rune' is classified as a Letter.
 func isLetter(ch rune) bool {
 	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= utf8.RuneSelf && unicode.IsLetter(ch)
 }
@@ -2571,33 +2564,26 @@ func StructOf(fields []StructField) Type {
 	var typ *structType
 	var ut *uncommonType
 
-	switch {
-	case len(methods) == 0:
+	if len(methods) == 0 {
 		t := new(structTypeUncommon)
 		typ = &t.structType
 		ut = &t.u
-	case len(methods) <= 4:
-		t := new(structTypeFixed4)
-		typ = &t.structType
-		ut = &t.u
-		copy(t.m[:], methods)
-	case len(methods) <= 8:
-		t := new(structTypeFixed8)
-		typ = &t.structType
-		ut = &t.u
-		copy(t.m[:], methods)
-	case len(methods) <= 16:
-		t := new(structTypeFixed16)
-		typ = &t.structType
-		ut = &t.u
-		copy(t.m[:], methods)
-	case len(methods) <= 32:
-		t := new(structTypeFixed32)
-		typ = &t.structType
-		ut = &t.u
-		copy(t.m[:], methods)
-	default:
-		panic("reflect.StructOf: too many methods")
+	} else {
+		// A *rtype representing a struct is followed directly in memory by an
+		// array of method objects representing the methods attached to the
+		// struct. To get the same layout for a run time generated type, we
+		// need an array directly following the uncommonType memory.
+		// A similar strategy is used for funcTypeFixed4, ...funcTypeFixedN.
+		tt := New(StructOf([]StructField{
+			{Name: "S", Type: TypeOf(structType{})},
+			{Name: "U", Type: TypeOf(uncommonType{})},
+			{Name: "M", Type: ArrayOf(len(methods), TypeOf(methods[0]))},
+		}))
+
+		typ = (*structType)(unsafe.Pointer(tt.Elem().Field(0).UnsafeAddr()))
+		ut = (*uncommonType)(unsafe.Pointer(tt.Elem().Field(1).UnsafeAddr()))
+
+		copy(tt.Elem().Field(2).Slice(0, len(methods)).Interface().([]method), methods)
 	}
 	// TODO(sbinet): Once we allow embedding multiple types,
 	// methods will need to be sorted like the compiler does.

gosrc/reflect/value.go

@@ -1031,7 +1031,7 @@ func (v Value) InterfaceData() [2]uintptr {
 func (v Value) IsNil() bool {
 	k := v.kind()
 	switch k {
-	case Chan, Func, Map, Ptr:
+	case Chan, Func, Map, Ptr, UnsafePointer:
 		if v.flag&flagMethod != 0 {
 			return false
 		}
@@ -1115,14 +1115,7 @@ func (v Value) MapIndex(key Value) Value {
 	typ := tt.elem
 	fl := (v.flag | key.flag).ro()
 	fl |= flag(typ.Kind())
-	if !ifaceIndir(typ) {
-		return Value{typ, *(*unsafe.Pointer)(e), fl}
-	}
-	// Copy result so future changes to the map
-	// won't change the underlying value.
-	c := unsafe_New(typ)
-	typedmemmove(typ, c, e)
-	return Value{typ, c, fl | flagIndir}
+	return copyVal(typ, fl, e)
 }
 
 // MapKeys returns a slice containing all the keys present in the map,
@@ -1152,20 +1145,96 @@ func (v Value) MapKeys() []Value {
 			// we can do about it.
 			break
 		}
-		if ifaceIndir(keyType) {
-			// Copy result so future changes to the map
-			// won't change the underlying value.
-			c := unsafe_New(keyType)
-			typedmemmove(keyType, c, key)
-			a[i] = Value{keyType, c, fl | flagIndir}
-		} else {
-			a[i] = Value{keyType, *(*unsafe.Pointer)(key), fl}
-		}
+		a[i] = copyVal(keyType, fl, key)
 		mapiternext(it)
 	}
 	return a[:i]
 }
 
+// A MapIter is an iterator for ranging over a map.
+// See Value.MapRange.
+type MapIter struct {
+	m  Value
+	it unsafe.Pointer
+}
+
+// Key returns the key of the iterator's current map entry.
+func (it *MapIter) Key() Value {
+	if it.it == nil {
+		panic("MapIter.Key called before Next")
+	}
+	if mapiterkey(it.it) == nil {
+		panic("MapIter.Key called on exhausted iterator")
+	}
+
+	t := (*mapType)(unsafe.Pointer(it.m.typ))
+	ktype := t.key
+	return copyVal(ktype, it.m.flag.ro()|flag(ktype.Kind()), mapiterkey(it.it))
+}
+
+// Value returns the value of the iterator's current map entry.
+func (it *MapIter) Value() Value {
+	if it.it == nil {
+		panic("MapIter.Value called before Next")
+	}
+	if mapiterkey(it.it) == nil {
+		panic("MapIter.Value called on exhausted iterator")
+	}
+
+	t := (*mapType)(unsafe.Pointer(it.m.typ))
+	vtype := t.elem
+	return copyVal(vtype, it.m.flag.ro()|flag(vtype.Kind()), mapitervalue(it.it))
+}
+
+// Next advances the map iterator and reports whether there is another
+// entry. It returns false when the iterator is exhausted; subsequent
+// calls to Key, Value, or Next will panic.
+func (it *MapIter) Next() bool {
+	if it.it == nil {
+		it.it = mapiterinit(it.m.typ, it.m.pointer())
+	} else {
+		if mapiterkey(it.it) == nil {
+			panic("MapIter.Next called on exhausted iterator")
+		}
+		mapiternext(it.it)
+	}
+	return mapiterkey(it.it) != nil
+}
+
+// MapRange returns a range iterator for a map.
+// It panics if v's Kind is not Map.
+//
+// Call Next to advance the iterator, and Key/Value to access each entry.
+// Next returns false when the iterator is exhausted.
+// MapRange follows the same iteration semantics as a range statement.
+//
+// Example:
+//
+//	iter := reflect.ValueOf(m).MapRange()
+// 	for iter.Next() {
+//		k := iter.Key()
+//		v := iter.Value()
+//		...
+//	}
+//
+func (v Value) MapRange() *MapIter {
+	v.mustBe(Map)
+	return &MapIter{m: v}
+}
+
+// copyVal returns a Value containing the map key or value at ptr,
+// allocating a new variable as needed.
+func copyVal(typ *rtype, fl flag, ptr unsafe.Pointer) Value {
+	if ifaceIndir(typ) {
+		// Copy result so future changes to the map
+		// won't change the underlying value.
+		c := unsafe_New(typ)
+		typedmemmove(typ, c, ptr)
+		return Value{typ, c, fl | flagIndir}
+	}
+	return Value{typ, *(*unsafe.Pointer)(ptr), fl}
+}
+
 // Method returns a function value corresponding to v's i'th method.
 // The arguments to a Call on the returned function should not include
 // a receiver; the returned function will always use v as the receiver.
@@ -2584,6 +2653,9 @@ func mapiterinit(t *rtype, m unsafe.Pointer) unsafe.Pointer
 //go:noescape
 func mapiterkey(it unsafe.Pointer) (key unsafe.Pointer)
 
+//go:noescape
+func mapitervalue(it unsafe.Pointer) (value unsafe.Pointer)
+
 //go:noescape
 func mapiternext(it unsafe.Pointer)
 
@@ -2595,6 +2667,8 @@ func maplen(m unsafe.Pointer) int
 // back into arg+retoffset before returning. If copying result bytes back,
 // the caller must pass the argument frame type as argtype, so that
 // call can execute appropriate write barriers during the copy.
+//
+//go:linkname call runtime.reflectcall
 func call(argtype *rtype, fn, arg unsafe.Pointer, n uint32, retoffset uint32)
 
 func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)