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sandersnsandersn
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Merge pull request #10374 from Microsoft/readonly-array-type-argument-assignability
Improve ReadonlyArray<T>.concat to match Array<T>
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‎src/lib/es5.d.ts

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@@ -1006,7 +1006,12 @@ interface ReadonlyArray<T> {
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* Combines two or more arrays.
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* @param items Additional items to add to the end of array1.
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*/
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concat(...items: T[]): T[];
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concat(...items: T[][]): T[];
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/**
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* Combines two or more arrays.
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* @param items Additional items to add to the end of array1.
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*/
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concat(...items: (T | T[])[]): T[];
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/**
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* Adds all the elements of an array separated by the specified separator string.
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* @param separator A string used to separate one element of an array from the next in the resulting String. If omitted, the array elements are separated with a comma.

‎tests/baselines/reference/arrayOfSubtypeIsAssignableToReadonlyArray.errors.txt

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tests/cases/compiler/arrayOfSubtypeIsAssignableToReadonlyArray.ts(13,1): error TS2322: Type 'A[]' is not assignable to type 'ReadonlyArray<B>'.
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Types of property 'concat' are incompatible.
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Type '{ (...items: A[][]): A[]; (...items: (A | A[])[]): A[]; }' is not assignable to type '{ <U extends ReadonlyArray<B>>(...items: U[]): B[]; (...items: B[][]): B[]; (...items: (B | B[])[]): B[]; }'.
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Type 'A[]' is not assignable to type 'B[]'.
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Type 'A' is not assignable to type 'B'.
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Property 'b' is missing in type 'A'.
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tests/cases/compiler/arrayOfSubtypeIsAssignableToReadonlyArray.ts(18,1): error TS2322: Type 'C<A>' is not assignable to type 'ReadonlyArray<B>'.
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Types of property 'concat' are incompatible.
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Type '{ (...items: A[][]): A[]; (...items: (A | A[])[]): A[]; }' is not assignable to type '{ <U extends ReadonlyArray<B>>(...items: U[]): B[]; (...items: B[][]): B[]; (...items: (B | B[])[]): B[]; }'.
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Type 'A[]' is not assignable to type 'B[]'.
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Type 'A' is not assignable to type 'B'.
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==== tests/cases/compiler/arrayOfSubtypeIsAssignableToReadonlyArray.ts (2 errors) ====
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class A { a }
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class B extends A { b }
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class C<T> extends Array<T> { c }
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declare var ara: A[];
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declare var arb: B[];
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declare var cra: C<A>;
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declare var crb: C<B>;
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declare var rra: ReadonlyArray<A>;
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declare var rrb: ReadonlyArray<B>;
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rra = ara;
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rrb = arb; // OK, Array<B> is assignable to ReadonlyArray<A>
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rra = arb;
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rrb = ara; // error: 'A' is not assignable to 'B'
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~~~
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!!! error TS2322: Type 'A[]' is not assignable to type 'ReadonlyArray<B>'.
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!!! error TS2322: Types of property 'concat' are incompatible.
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!!! error TS2322: Type '{ (...items: A[][]): A[]; (...items: (A | A[])[]): A[]; }' is not assignable to type '{ <U extends ReadonlyArray<B>>(...items: U[]): B[]; (...items: B[][]): B[]; (...items: (B | B[])[]): B[]; }'.
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!!! error TS2322: Type 'A[]' is not assignable to type 'B[]'.
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!!! error TS2322: Type 'A' is not assignable to type 'B'.
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!!! error TS2322: Property 'b' is missing in type 'A'.
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rra = cra;
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rra = crb; // OK, C<B> is assignable to ReadonlyArray<A>
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rrb = crb;
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rrb = cra; // error: 'A' is not assignable to 'B'
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~~~
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!!! error TS2322: Type 'C<A>' is not assignable to type 'ReadonlyArray<B>'.
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!!! error TS2322: Types of property 'concat' are incompatible.
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!!! error TS2322: Type '{ (...items: A[][]): A[]; (...items: (A | A[])[]): A[]; }' is not assignable to type '{ <U extends ReadonlyArray<B>>(...items: U[]): B[]; (...items: B[][]): B[]; (...items: (B | B[])[]): B[]; }'.
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!!! error TS2322: Type 'A[]' is not assignable to type 'B[]'.
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!!! error TS2322: Type 'A' is not assignable to type 'B'.
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‎tests/baselines/reference/arrayOfSubtypeIsAssignableToReadonlyArray.js

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//// [arrayOfSubtypeIsAssignableToReadonlyArray.ts]
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class A { a }
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class B extends A { b }
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class C<T> extends Array<T> { c }
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declare var ara: A[];
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declare var arb: B[];
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declare var cra: C<A>;
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declare var crb: C<B>;
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declare var rra: ReadonlyArray<A>;
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declare var rrb: ReadonlyArray<B>;
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rra = ara;
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rrb = arb; // OK, Array<B> is assignable to ReadonlyArray<A>
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rra = arb;
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rrb = ara; // error: 'A' is not assignable to 'B'
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rra = cra;
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rra = crb; // OK, C<B> is assignable to ReadonlyArray<A>
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rrb = crb;
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rrb = cra; // error: 'A' is not assignable to 'B'
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//// [arrayOfSubtypeIsAssignableToReadonlyArray.js]
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var __extends = (this && this.__extends) || function (d, b) {
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for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
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function __() { this.constructor = d; }
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d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
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};
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var A = (function () {
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function A() {
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}
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return A;
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}());
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var B = (function (_super) {
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__extends(B, _super);
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function B() {
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_super.apply(this, arguments);
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}
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return B;
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}(A));
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var C = (function (_super) {
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__extends(C, _super);
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function C() {
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_super.apply(this, arguments);
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}
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return C;
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}(Array));
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rra = ara;
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rrb = arb; // OK, Array<B> is assignable to ReadonlyArray<A>
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rra = arb;
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rrb = ara; // error: 'A' is not assignable to 'B'
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rra = cra;
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rra = crb; // OK, C<B> is assignable to ReadonlyArray<A>
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rrb = crb;
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rrb = cra; // error: 'A' is not assignable to 'B'

‎tests/cases/compiler/arrayOfSubtypeIsAssignableToReadonlyArray.ts

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class A { a }
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class B extends A { b }
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class C<T> extends Array<T> { c }
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declare var ara: A[];
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declare var arb: B[];
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declare var cra: C<A>;
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declare var crb: C<B>;
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declare var rra: ReadonlyArray<A>;
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declare var rrb: ReadonlyArray<B>;
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rra = ara;
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rrb = arb; // OK, Array<B> is assignable to ReadonlyArray<A>
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rra = arb;
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rrb = ara; // error: 'A' is not assignable to 'B'
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rra = cra;
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rra = crb; // OK, C<B> is assignable to ReadonlyArray<A>
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rrb = crb;
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rrb = cra; // error: 'A' is not assignable to 'B'

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