What is a method group in C#?

I have often encountered an error such as “cannot convert from ‘method group’ to ‘string'” in cases like:

var list = new List<string>();
// ... snip
list.Add(someObject.ToString);

of course there was a typo in the last line because I forgot the invocation parentheses after ToString. The correct form would be:

var list = new List<string>();
// ... snip
list.Add(someObject.ToString()); // <- notice the parentheses

However I came to wonder what is a method group. Google isn’t much of a help nor MSDN.

Answer

A method group is the name for a set of methods (that might be just one) – i.e. in theory the ToString method may have multiple overloads (plus any extension methods): ToString(), ToString(string format), etc – hence ToString by itself is a “method group”.

It can usually convert a method group to a (typed) delegate by using overload resolution – but not to a string etc; it doesn’t make sense.

Once you add parentheses, again; overload resolution kicks in and you have unambiguously identified a method call.

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