Edit Question - KnowledgeHub

Title Body

It all started with a trick question that someone posed to me.. (It's mentioned in the book - C# in a nutshell) Here's the gist of it. Double a = Double.NaN; Console.WriteLine(a == a); // => false Console.WriteLine(a.Equals(a)); // => true The above doesn't seem right. a should always be == to itself (reference equality) & both should be consistent. Seems like Double overloads the == operator. Confirmed by reflector as follows: [__DynamicallyInvokable] public static bool operator ==(double left, double right) { return (left == right); } Strange that looks recursive and no mention of the NaN specific behavior. So why does it return false? So I add some more code to distinguish var x = "abc"; var y = "xyz"; Console.WriteLine(x == y); // => false Now I see L_0001: ldc.r8 NaN L_000a: stloc.0 L_000b: ldloc.0 L_000c: ldloc.0 L_000d: ceq L_000f: call void [mscorlib]System.Console::WriteLine(bool) L_0014: nop L_0015: ldloca.s a L_0017: ldloc.0 L_0018: call instance bool [mscorlib]System.Double::Equals(float64) L_001d: call void [mscorlib]System.Console::WriteLine(bool) L_0022: nop L_0023: ldstr "abc" L_0028: stloc.1 L_0029: ldstr "xyz" L_002e: stloc.2 L_002f: ldloc.1 L_0030: ldloc.2 L_0031: call bool [mscorlib]System.String::op_Equality(string, string) L_0036: call void [mscorlib]System.Console::WriteLine(bool) for doubles, the == operator call translates to a ceq IL opcode where as for strings, it translates to System.String::op_Equality(string, string). Sure enough the documentation for ceq specifies that it is special-cased for floating point num

Tags (comma-separated) Cancel