why does equals not work the same when items are cast to object?

Question

when i cast int and float to object and compare them the equality is always false. Why?

        float f = 0.0f;
        int i = 0;
        Console.WriteLine(f.Equals(i)); // true
        Console.WriteLine(i.Equals(f)); // false
        Console.WriteLine(i == f); // true
        Console.WriteLine("----------------");
        object obf = f;
        object obi = i;
        Console.WriteLine(obf.Equals(obi)); // false
        Console.WriteLine(obi.Equals(obf)); // false
        Console.WriteLine(obi == obf); // false
        Console.WriteLine("----------------");

Update: this is NOT the case for the same type

        int i1 = 1;
        int i2 = 1;
        object oi1 = i1;
        object oi2 = i2;
        Console.WriteLine(oi1.Equals(oi2)); // true
        Console.WriteLine(oi2.Equals(oi1)); // true

Answer 1

A float is only equal to another float, and an int is only equal to another int. The only lines which are returning true are these ones:

Console.WriteLine(f.Equals(i));
Console.WriteLine(i == f);

In both of these cases, there's an implicit conversion of the value of i to float, so they're equivalent to:

Console.WriteLine(f.Equals((float) i));
Console.WriteLine((float) i == f);

These conversions are just normal conversions required for overload resolution of methods and operators.

None of the rest of the lines involve that implicit conversion, so they're comparing the two different types, which gives a result of false even when it is comparing by value (which is the case with all the Equals calls). That's why using Equals on the boxed int values does return true, because that's comparing two values of the same type, by value.

In this case:

Console.WriteLine(obi == obf);

it's not even trying to compare numeric values - it's comparing the references for the boxed objects. As there are two different references, the result is false - and would be even if both values were of type int.

Answer 2

Others have already explained why == does not work as expected on your objects.

Regarding your edit: oi1.Equals(oi2) works because Equals is a virtual function and, thus, Int32.Equals(object) is called, whose return value is defined as follows:

true if obj is an instance of Int32 and equals the value of this instance; otherwise, false.

This also explains why obi.Equals(obf)) returns false: obf is not an instance of Int32.