Question

I was just participating in Stack Overflow question Is everything in .NET an object?.

And one poster (in comments of accepted answer) seemed to think that performing a method call on a value type resulted in boxing. He pointed me to Boxing and Unboxing (C# Programming Guide) which doesn’t exactly specify the use case we’re describing.

I’m not one to trust a single source, so I just wanted to get further feedback on the question. My intuition is that there is no boxing but my intuition does suck. 😀

To further elaborate:

The example I used was:

int x = 5; string s = x.ToString(); // Boxing?? 

Boxing does not occur if the struct in question overrides the method inherited from the object as the accepted answer here states.

However if the struct doesn’t override the method, a ‘constrain’ CIL command is executed prior to a callvirt. According to the documentation, OpCodes.Constrained Field, this results in boxing:

If thisType is a value type and thisType does not implement method then ptr is dereferenced, boxed, and passed as the ‘this’ pointer to the callvirt method instruction.

Answer 1

Here’s the IL for your code:

L_0001: ldc.i4.5      // get a 5 on the stack L_0002: stloc.0       // store into x L_0003: ldloca.s x    // get the address of x on the stack L_0005: call instance string [mscorlib]System.Int32::ToString()  // ToString L_000a: stloc.1       // store in s 

So the answer in this case is no.