Compare boxed objects in C#

Question

Is it possible to compare two objects without knowing their boxed types at compile time? For instance, if I have a object{long} and object{int}, is there a way to know if the boxed values are equal?

My method retrieves two generic objects, and there's no way to know what their inner types are at compile time. Right now, the comparison is made by the following code:

_keyProperties[x].GetValue(entity, null).Equals(keyValues[x])

where, say, _keyProperties[x].GetValue(entity, null) is a object{long} and keyValues[x] is a object{int} (but they can be inverted as well).

I need this because I am building a mock repository for my unit tests, and I have started by including a generic repository implementation as described here. This implementation compares two generic fake-DB keys in its Find method.

Have you seen [this answer](http://stackoverflow.com/a/6669045/728795), especially its second part? — Andrei, Jun 12 '13 at 08:30
Of course I did, but I am getting a `System.InvalidCastException` with the message "Cannot convert a null object into a value type". — frapontillo, Jun 12 '13 at 08:38
I don't think so, because the values I'm trying to cast in my tests are not null. — frapontillo, Jun 12 '13 at 08:46

score 2 · Accepted Answer · edited May 23 '17 at 12:25

2

This might be too slow for your case, but you can use dynamic to do the test as the following code demonstrates:

object obj1 = 1;
object obj2 = 1.0;

if (obj1.Equals(obj2))
    Console.WriteLine("Yes");
else
    Console.WriteLine("No"); // Prints "No" as you'd expect.

if ((dynamic) obj1 == (dynamic) obj2)
    Console.WriteLine("Yes"); // Prints "Yes" because it handles trivial conversions.
else
    Console.WriteLine("No");

Be aware that using dynamic can be slow (although the code generated to support it is cached so at least that part is not performed more than once).

Also it can have some problems if the types are not related - see here for more discussion.

For example, this will throw an exception:

object obj1 = "Hello";
object obj2 = 1.0;

if ((dynamic) obj1 == (dynamic) obj2) // Throws an exception!
    Console.WriteLine("Yes");
else
    Console.WriteLine("No");

edited May 23 '17 at 12:25

Community

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answered Jun 12 '13 at 08:34

Matthew Watson

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That could be a solution, but I'm making the comparison inside an expression tree, and "An expression tree may not contain a dynamic operation" is the compile error I get. – frapontillo Jun 12 '13 at 08:47
1

@frapontillo Ah that's a shame, sorry! – Matthew Watson Jun 12 '13 at 08:49
Still, this is funny: by exporting the comparison code inside a method, the compiler does not whine about it and the comparison works! Thank you very much! I really don't care about speed, as the comparison will be done in tests where I don't care about it that much. – frapontillo Jun 12 '13 at 08:55

Compare boxed objects in C#

1 Answers1