What is a method group in C#?

Question

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 round paranthesis after "ToString". The correct form would be :

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

However I came to wonder what is a method group. Google isn't much of a help and MSDN neither.

Answer 1

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

Answer 2

The first result in your MSDN search said

The method group identifies the one method to invoke or the set of overloaded methods from which to choose a specific method to invoke

my understanding is that basically because when you just write someInteger.ToString, it may refer to

Int32.ToString(IFormatProvider)

or it can refer to

Int32.ToString()

so it is called a method group

Answer 3

The ToString function has many overloads - the method group would be the group consisting of all the different overloads for that function.

Answer 4

Also, if you are using linq, you can apparently do something like myList.select(methodGroup);

So, for example, i have

private string DoSomethingToMyString(string input){ //blah blah }

public list GetStringStuff(){ return something.getStringsFromSomewhere.select(DoSomethingToMyString); }