Instance equality

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 35933)
+++ runtime/vm/object.h	(working copy)
@@ -4130,7 +4130,17 @@
 // in Dart source code.
 class Instance : public Object {
  public:
-  virtual bool Equals(const Instance& other) const;
+  // Equality and identity testing.
+  // 1. OperatorEquals: true iff 'this == other' is true in Dart code.

[rmacnak, 2014/05/12 17:15:17]

Reminds me of Self's equivalent (=), indistinguishable (==), and identical
(===).

[koda, 2014/05/12 17:41:43]

Maybe we should add SameSameButDifferent :)

+  // 2. IsIdenticalTo: true iff 'identical(this, other)' is true in Dart code.
+  // 3. CanonicalizeEquals: used to canonicalize compile-time constants, e.g.,

[hausner, 2014/05/12 17:09:30]

Would it make sense to rename this as BitwiseEquals throughout?

[koda, 2014/05/12 17:41:43]

That is almost true, but not technically true for GrowableObjectArray, where it
actually looks inside its single Array field. Also, there still seems to be some
dispute about whether we really should canonicalize NaNs using bitwise equality
(issue 18738).

I mostly want to minimize the risk that people make false assumptions.

+  //    using bitwise equality of fields and list elements.
+  // Subclasses where 1 and 3 coincide may also define a plain Equals, e.g.,
+  // String and Integer.
+  virtual bool OperatorEquals(const Instance& other) const;
+  bool IsIdenticalTo(const Instance& other) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const;
+
   // Returns Instance::null() if instance cannot be canonicalized.
   // Any non-canonical number of string will be canonicalized here.
   // An instance cannot be canonicalized if it still contains non-canonical
@@ -4160,10 +4170,6 @@
                     const TypeArguments& type_instantiator,
                     Error* bound_error) const;
 
-  // Check whether this instance is identical to the argument according to the
-  // specification of dare:core's identical().
-  bool IsIdenticalTo(const Instance& other) const;
-
   bool IsValidNativeIndex(int index) const {
     return ((index >= 0) && (index < clazz()->ptr()->num_native_fields_));
   }
@@ -4308,6 +4314,9 @@
   virtual RawTypeArguments* arguments() const;
   virtual intptr_t token_pos() const;
   virtual bool IsInstantiated(GrowableObjectArray* trail = NULL) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const {
+    return Equals(other);
+  }
   virtual bool Equals(const Instance& other) const {
     return IsEquivalent(other);
   }
@@ -4874,6 +4883,17 @@
                          Heap::Space space = Heap::kNew,
                          const bool silent = false);
 
+  virtual bool OperatorEquals(const Instance& other) const {
+    return Equals(other);
+  }
+  virtual bool CanonicalizeEquals(const Instance& other) const {
+    return Equals(other);
+  }
+  virtual bool Equals(const Instance& other) const {
+    UNREACHABLE();
+    return false;
+  }
+
   // Integer is an abstract class.
   virtual bool IsZero() const {
     UNREACHABLE();
@@ -5138,8 +5158,9 @@
     return raw_ptr()->value_;
   }
 
-  bool EqualsToDouble(double value) const;
-  virtual bool Equals(const Instance& other) const;
+  bool BitwiseEqualsToDouble(double value) const;
+  virtual bool OperatorEquals(const Instance& other) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const;
 
   static RawDouble* New(double d, Heap::Space space = Heap::kNew);
 
@@ -5259,6 +5280,12 @@
   // Compares to an array of UTF-32 encoded characters.
   bool Equals(const int32_t* characters, intptr_t len) const;
 
+  virtual bool OperatorEquals(const Instance& other) const {
+    return Equals(other);
+  }
+  virtual bool CanonicalizeEquals(const Instance& other) const {
+    return Equals(other);
+  }
   virtual bool Equals(const Instance& other) const;
 
   intptr_t CompareTo(const String& other) const;
@@ -5889,7 +5916,7 @@
     StorePointer(&raw_ptr()->type_arguments_, value.raw());
   }
 
-  virtual bool Equals(const Instance& other) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const;
 
   static const intptr_t kBytesPerElement = kWordSize;
   static const intptr_t kMaxElements = kSmiMax / kBytesPerElement;
@@ -6049,7 +6076,7 @@
     StorePointer(&raw_ptr()->type_arguments_, value.raw());
   }
 
-  virtual bool Equals(const Instance& other) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const;
 
   virtual RawInstance* CheckAndCanonicalize(const char** error_str) const {
     UNREACHABLE();
@@ -6760,7 +6787,7 @@
   static RawJSRegExp* FromDataStartAddress(void* data);
   const char* Flags() const;
 
-  virtual bool Equals(const Instance& other) const;
+  virtual bool CanonicalizeEquals(const Instance& other) const;
 
   static const intptr_t kBytesPerElement = 1;
   static const intptr_t kMaxElements = kSmiMax / kBytesPerElement;