Cannot convert from type T to type T?

A strange error here using static factory pattern. What am I missing? Here is the code:

class subclass<T> extends immutablestruct<T>{
private immutablestruct f;
private T x;

    //constru开发者_运维问答ctor
<T> subclass(T y, immutablestruct<T> f ){
    this.x = y;  //this is there the error is
    this.f = f;
}

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Remove <T> from constructor declaration. Now you're declaring second generic parameter, while you can access old T value:

//constructor
subclass(T y, immutablestruct<T> f ){