Question: How to get the the generic type of Array?

[LiaoPeng]

The requirement is to create obj by generic type.

class A { }
function createObj<T>(): T {
    var isArr = isArray<T>();
    if (isArr) {
        let arr = {} as T;
        // Is there a way to create an instance of A and push the instance to the `arr`
       return arr;
    }
    // other logic
}
createObj<Array<A>>();

[dcodeIO]

<T>{] should work to create an instance using the default constructor (the one without arguments). Doesn't it?

Possibly related: #258

[LiaoPeng]

@dcodeIO Thanks for you reply.
The above code, the generic T represented Array<A>. Is there a way to create an instance of A in function createObj<T>():T. I want to create an array with some elements.

[dcodeIO]

At this point I think that there must be a constructor with zero arguments for it to work, that is until this TODO has been addressed.

[LiaoPeng]

@dcodeIO Thanks for you reply.
// TODO: if the constructor requires parameters, check whether these are given as part of the object literal and use them to call the ctor while not generating a store.

1. If the constructor requires parameters, the {} not providers parameters. Not generating a store, so creating an instance without using constructor. It maybe lead to create an unsafe instance if the constructor has some restrictions. eg:

class A{
      year: i32;
      constructor(a: i32) {
              if ( a < 1900) {
                   this.year = 1900;
              }
             this.year = a;
      }
}

In that case calling the ctor with default parameter value (basic type value is 0, object type is null or {}) maybe a choice.

[MaxGraey]

@dcodeIO Could we close this for now?

[dcodeIO]

Yeah, seems this is pretty similar to #262, which is our tracking issue now.

[trusktr]

#262 is this very issue. Did you mean #258?

[trusktr]

Just my sentiment here, but stuff like isArray<T>() is a bit awkward and straying away from the TypeScript language. My IDE treats it as an error, and plus isn't portable.

Is there another way to allow the same thing in AS, while being compatible with TypeScript?

[MaxGraey]

isArray(expr) is portable, isArray<T>() - isn't. Also you could use Array.isArray(arr)