使用多个泛型类型调用泛型方法而不指定每个泛型类型

Question

So what I have is a generic Method with multiple generic types.

Now I'd like to call this Method this way (using the types of a and b and just specifying the return type):

class Example
{

    T1 GenericMethod<T1, T2, T3>(T2 parameter1, T3 parameter2)

    {
        T1 returnValue = default(T1);

        // ... Do something with returnType, parameter1 and parameter2

        return returnValue;
    }

    void AccessGenericMethod()
    {
        var a = new Foo1();
        var b = new Foo2();
        var result = GenericMethod<ReturnType>(a, b); // doesn't work
    }
}

And i would like to avoid to call GenericMethod this way

var result GenericMethod<ReturnType, Foo1, Foo2>(a, b);

Answer 1

In C#, there is no partial type inference: You must either specify all or none of the generic arguments, but the latter only works if the compiler is able to infer all types from context. Return types cannot be infered (except for some special cases such as lambdas), so what you want to do is not possible.

Two workarounds:

A: Move T1 from the method to the class

class Example<T1>
{
    T1 GenericMethod<T2, T3>(T2 parameter1, T3 parameter2)

B: Replace T2 and T3 by object

class Example
{
    T1 GenericMethod<T1>(object parameter1, object parameter2)

Answer 2

I found a solution

class Example
{
    T1 GenericMethod<T1, T2, T3>(T2 parameter1, T3 parameter2, out T1 returnValue)
    {
        returnValue = default(T1);

        // ... Do something with returnType, parameter1 and parameter2

        return returnValue = new T1();
    }

    void AccessGenericMethod()
    {
        var a = new Foo1();
        var b = new Foo2();
        GenericMethod(a, b, out ReturnType result1); // work!
        ReturnType result2 = GenericMethod(a, b, out result2);
    }
}