用于Object.Equals的IL代码生成

Question

Even though the type resolved to Int32 at runtime, the IL shows it called object.equals instead of int32.Equals, like this example:

object x = 5;
object y = 5;
Console.WriteLine(x.Equals(y));

But it returns True, that means it performed a value equality. I guess my question is shouldn't IL should have been instance bool [mscorlib]System.Int32::Equals(int32)

// [18 13 - 18 27]
IL_0001: ldc.i4.5     
IL_0002: box          [mscorlib]System.Int32
IL_0007: stloc.0      // x

// [19 13 - 19 27]
IL_0008: ldc.i4.5     
IL_0009: box          [mscorlib]System.Int32
IL_000e: stloc.1      // y
// [21 13 - 21 46]
IL_000f: ldloc.0      // x
IL_0010: ldloc.1      // y
IL_0011: callvirt     instance bool [mscorlib]System.Object::Equals(object)
IL_0016: call         void [mscorlib]System.Console::WriteLine(bool)
IL_001b: nop          

Answer 1

The object.Equals method is virtual, and is overridden in Int32 . callvirt is a polymorphic call - it will check the run-time type of the object before calling a virtual method, and use the correct implementation.

Int32 implements IEquatable<T> interface and defines another overload of Equals

public bool Equals(Int32 obj);

The compiler can choose this overload only if the compile-time types of both the parameter and the value it's called on is Int32 . Here, the compile-time types are object , so the compiler can only use the object.Equals(object obj) overload.