What is the difference between == and Equals() for primitives in C#?

Question

Consider this code:

int age = 25;
short newAge = 25;
Console.WriteLine(age == newAge);  //true
Console.WriteLine(newAge.Equals(age)); //false
Console.ReadLin         


        

Answer 1

What you need to realize is that doing == will always end up calling a method. The question is whether calling == and Equals ends up calling/doing the same things.

With reference types, == will always 1st check whether the references are the same (Object.ReferenceEquals). Equals on the other hand can be overridden and may check whether some values are equal.

EDIT: to answer svick and add on SLaks comment, here is some IL code

int i1 = 0x22; // ldc.i4.s ie pushes an int32 on the stack
int i2 = 0x33; // ldc.i4.s 
short s1 = 0x11; // ldc.i4.s (same as for int32)
short s2 = 0x22; // ldc.i4.s 

s1 == i1 // ceq
i1 == s1 // ceq
i1 == i2 // ceq
s1 == s2 // ceq
// no difference between int and short for those 4 cases,
// anyway the shorts are pushed as integers.

i1.Equals(i2) // calls System.Int32.Equals
s1.Equals(s2) // calls System.Int16.Equals
i1.Equals(s1) // calls System.Int32.Equals: s1 is considered as an integer
// - again it was pushed as such on the stack)
s1.Equals(i1) // boxes the int32 then calls System.Int16.Equals
// - int16 has 2 Equals methods: one for in16 and one for Object.
// Casting an int32 into an int16 is not safe, so the Object overload
// must be used instead.