I have seen similar questions to this, but they involve different types so I think this is a new question.
Consider the following code:
public void Test(bool value)
{
// The following line provokes a compiler error:
// "Type of conditional expression cannot be determined because there is
// no implicit conversion between 'method group' and 'method group".
Func<bool> test = value ? F : F;
}
public bool F()
{
return false;
}
Now, according to the C# 3.0 Standard,
The second and third operands of the
?: operator control the type of the
conditional expression. Let X and Y be
the types of the second and third
operands. Then,
If X and Y are the same type, then
this is the type of the conditional
Otherwise, if an implicit conversion
(§6.1) exists from X to Y, but not
from Y to X, then Y is the type of the
conditional expression. Otherwise, if
an implicit conversion (§6.1) exists
from Y to X, but not from X to Y, then
X is the type of the conditional
expression. Otherwise, no expression
type can be determined, and a
compile-time error occurs.
It seems to me that in my sample code, X and Y must be of the same type, since they are the selfsame entity, Func. So why does it not compile?
Brian Rasmussen :
The question was changed significantly, so my original answer is a bit off by now. \n\nHowever, the problem is essentially the same. I.e. there could be any number of matching delegate declarations for F and since there is no implicit conversion between two identical delegate declarations the type of F cannot be converted to Func<bool>.\n\nLikewise, if you declare \n\nprivate delegate void X();\nprivate delegate void Y();\nprivate static void Foo() {}\n\n\nYou cannot do \n\nX x = Foo;\nY y = x;\n\n\n\n\nOriginal answer:\n\nIt doesn't work because method groups cannot be assigned to an implicitly typed variable.\n\nvar test = Func; doesn't work either. \n\nThe reason being that there could be any number of delegate types for Func. E.g. Func matches both of these declarations (in addition to Action) \n\nprivate delegate void X();\nprivate delegate void Y();\n\n\nTo use implicitly typed variables with method groups, you need to remove the ambiguity by casting. \n\n\n\nSee archil's answer for a concrete example of one way to fix this. That is, he shows what the corrected code might look like [assuming the delegate you desire to match is Action].",
2011-05-16T10:04:51