Is replacing an optional parameter with overloads a breaking change?

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I thought that was a good question, so here goes my take.

Using a quick client that does this:

        c1.Foo(1);
        c1.Foo(1, 2);

When using optional parameter the client IL looks like:

    IL_0000: nop
IL_0001: newobj instance void [ClassLibrary1]ClassLibrary1.Class1::.ctor()
IL_0006: stloc.0
IL_0007: ldloc.0
IL_0008: ldc.i4.1
IL_0009: ldc.i4.5
IL_000a: callvirt instance void [ClassLibrary1]ClassLibrary1.Class1::Foo(int32, int32)
IL_000f: nop
IL_0010: ldloc.0
IL_0011: ldc.i4.1
IL_0012: ldc.i4.2
IL_0013: callvirt instance void [ClassLibrary1]ClassLibrary1.Class1::Foo(int32, int32)
IL_0018: nop
IL_0019: ret

and when using overloads it looks like:

    IL_0000: nop
IL_0001: newobj instance void [ClassLibrary2]ClassLibrary2.Class2::.ctor()
IL_0006: stloc.0
IL_0007: ldloc.0
IL_0008: ldc.i4.1
IL_0009: callvirt instance void [ClassLibrary2]ClassLibrary2.Class2::Foo(int32)
IL_000e: nop
IL_000f: ldloc.0
IL_0010: ldc.i4.1
IL_0011: ldc.i4.2
IL_0012: callvirt instance void [ClassLibrary2]ClassLibrary2.Class2::Foo(int32, int32)
IL_0017: nop
IL_0018: ret

So, if you changed the implementation from optional to overloads, but left the client as it was originally, it would be effectively adding the default parameter for you, and always calling the the function that has two arguments, which may or may not be the desired behaviour.

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