As mentioned above, nilable cannot be specified for the actual type parameter of Generics.

This restriction causes the following new Test( val ) to fail.

// @lnsFront: skip
class Test<T> {
   let val:T;
}
let val:int! = 1;
let test = new Test( val ); // error

There are two patterns to avoid this error.

• Use T!
• Use the Nilable type

In the case of "using T!", the above processing can be written as follows.

// @lnsFront: skip
class Test<T> {
   let val:T!; // <--- T! とする
}
let val:int! = 1;
let test = new Test( val );

However, in many cases, even if non-nilable is fine, it has to be declared as nilable, so unwrap processing becomes necessary, which is troublesome.

That's why we use the Nilable type.