C#: Virtual Function invocation is even faster than a delegate invocation?

Question

It just happens to me about one code design question. Say, I have one \"template\" method that invokes some functions that may \"alter\". A intuitive design is to follow \"Templ

Answer 1

Think about what's required in each case:

Virtual call

• Check for nullity
• Navigate from object pointer to type pointer
• Look up method address in instruction table
• (Not sure - even Richter doesn't cover this) Go to base type if method isn't overridden? Recurse until we find the right method address. (I don't think so - see edit at bottom.)
• Push original object pointer onto stack ("this")
• Call method

Delegate call

• Check for nullity
• Navigate from object pointer to array of invocations (all delegates are potentially multicast)
• Loop over array, and for each invocation:
  • Fetch method address
  • Work out whether or not to pass the target as first argument
  • Push arguments onto stack (may have been done already - not sure)
  • Optionally (depending on whether the invocation is open or closed) push the invocation target onto the stack
  • Call method

There may be some optimisation so that there's no looping involved in the single-call case, but even so that will take a very quick check.

But basically there's just as much indirection involved with a delegate. Given the bit I'm unsure of in the virtual method call, it's possible that a call to an unoverridden virtual method in a massively deep type hierarchy would be slower... I'll give it a try and edit with the answer.

EDIT: I've tried playing around with both the depth of inheritance hierarchy (up to 20 levels), the point of "most derived overriding" and the declared variable type - and none of them seems to make a difference.

EDIT: I've just tried the original program using an interface (which is passed in) - that ends up having about the same performance as the delegate.