First of all “A method group is a set of overloaded methods resulting from a member lookup”. In my example I use the set of Console.WriteLine methods with 19 overloads.
The definition of a method group in C# Language Specification also states that: “A method group is permitted in an invocation-expression (§7.6.5) , a delegate-creation-expression (§7.6.10.5) and as the left hand side of an is operator, and can be implicitly converted to a compatible delegate type (§6.6).”
I could think of one scenario where this functionality could be useful:
Action<string> print = (Action<string>)Console.WriteLine;
print("Hello!");
if (Console.WriteLine is Action<string>)
{
Console.WriteLine("We're compatible!");
}
First couple of lines show that we can ‘cast’ a method group Console.WriteLine into a delegate. What actually happens is the “implicit conversion converted to a compatible delegate type”, which creates an instance of a delegate calling one of many overloaded Console.WriteLine methods with compatible signature.
So according to specs we could use the “left side of is operator” feature mentioned above to test if the method group is compatible with a given delegate type (implicit conversion exists). This is what is checked inside the ‘if’ statement in the sample code.
Surprisingly, the code compiles, but gives a warning “The given expression is never of the provided ('System.Action') type”. So it looks like there will be no attempts to check the compatibility of the method group and the delegate type at runtime.
Hence, my questions:
- Why are the methods groups allowed on the left-side of ‘is’ operator if the check cannot be performed at runtime?
- Why this construct gives a warning and not a compilation error?
- Are there any practical scenarios of using method groups on the left side of ‘is’ operator?
- Is this something reserved for future uses, i.e. it is envisaged that the code above will work someday?
