Why is Delphi unable to infer the type for a parameter TEnumerable<T>?
- by deepc
Consider the following declaration of a generic utility class in Delphi 2010:
TEnumerableUtils = class
public
class function InferenceTest<T>(Param: T): T;
class function Count<T>(Enumerable: TEnumerable<T>): Integer; overload;
class function Count<T>(Enumerable: TEnumerable<T>; Filter: TPredicate<T>): Integer; overload;
end;
Somehow the compiler type inference seems to have problems here:
var
I: Integer;
L: TList<Integer>;
begin
TEnumerableUtils.InferenceTest(I); // no problem here
TEnumerableUtils.Count(L); // does not compile: E2250 There is no overloaded version of 'Count' that can be called with these arguments
TEnumerableUtils.Count<Integer>(L); // compiles fine
end;
The first call works as expected and T is correctly inferred as Integer.
The second call does not work, unless I also add <Integer -- then it works, as can be seen in the third call. Am I doing something wrong or is the type inference in Delphi just not supporting this (I don't think it is a problem in Java which is why expected it to work in Delphi, too).
