Question

class Sample
{
    public static T M<T, TParam1>(TParam1 param1)
    {
        return default(T);
    }
}
class Program
{
    static void Main(string[] args)
    {

        double d = Sample.M((int)121);
    }
}

This code doesn’t compile and results in the following error message:

The type arguments for method
‘ThreadPoolTest.Sample.M(TParam1)’ cannot be inferred from
the usage. Try specifying the type arguments
explicitly

Why isn’t type inference working in this example?

Answer 1

Type inference can only use the arguments to the method call. The fact that you’re assigning the result to a double is entirely irrelevant as far as type inference is concerned. In other words, as far as the compiler is concerned, it needs to work out what this means:

Sample.M((int) 121)

without any more information. For example, you could mean Sample.M<int, int>, or Sample.M<double, int>, or Sample.M<string, int> – there’s no information so say which of those is a better match.

You don’t mention T in the parameter list, so type inference can’t help.