apparentTypeSubtyping.js

//// [apparentTypeSubtyping.ts]
// subtype checks use the apparent type of the target type
// S is a subtype of a type T, and T is a supertype of S, if one of the following is true, where S' denotes the apparent type (section 3.8.1) of S:

class Base<U extends String> {
    x: U;
}

// is String (S) a subtype of U extends String (T)? Would only be true if we used the apparent type of U (T)
class Derived<U> extends Base<string> { // error
    x: String;
}

class Base2 {
    x: String;
    static s: String;
}

// is U extends String (S) a subtype of String (T)? Apparent type of U is String so it succeeds
class Derived2<U extends String> extends Base2 { // error because of the prototype's not matching, not because of the instance side
    x: U;
}

//// [apparentTypeSubtyping.js]
// subtype checks use the apparent type of the target type
// S is a subtype of a type T, and T is a supertype of S, if one of the following is true, where S' denotes the apparent type (section 3.8.1) of S:
var __extendStatics = (this && this.__extendStatics) ||
    Object.setPrototypeOf ||
    ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
    function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
var __extends = (this && this.__extends) || function (d, b) {
    __extendStatics(d, b);
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
var Base = (function () {
    function Base() {
    }
    return Base;
}());
// is String (S) a subtype of U extends String (T)? Would only be true if we used the apparent type of U (T)
var Derived = (function (_super) {
    __extends(Derived, _super);
    function Derived() {
        return _super.apply(this, arguments) || this;
    }
    return Derived;
}(Base));
var Base2 = (function () {
    function Base2() {
    }
    return Base2;
}());
// is U extends String (S) a subtype of String (T)? Apparent type of U is String so it succeeds
var Derived2 = (function (_super) {
    __extends(Derived2, _super);
    function Derived2() {
        return _super.apply(this, arguments) || this;
    }
    return Derived2;
}(Base2));