2.4: Readonly<Map<k,v>> vs. ReadonlyMap<k,v>

TypeScript Version: 2.4.1

Code

function GenMap() : ReadonlyMap<string, number> {
    const theMap = new Map<string, number>();
    theMap.set("one", 1);
    theMap.set("two", 2);
    return Object.freeze(theMap);
}

Expected behavior: Compiles without error in tsc@<2.4.0

Actual behavior:

TryX.ts(5,5): error TS2322: Type 'Readonly<Map<string, number>>' is not assignable to type 'ReadonlyMap<s
tring, number>'.
  Property '[Symbol.iterator]' is missing in type 'Readonly<Map<string, number>>'.

[NaridaL]

@mhegazy , as @sylvanaar 's comment/link shows, calling Object.freeze on a map doesn’t actually stop new keys being added with .set(). Do the suggested overloads still make sense in this case?

[ThomasdenH]

Readonly<Map<_, _>> is not the same as ReadonlyMap<_, _>. I think the latter is a subset of the former, so the best solution would be to make Readonly<Map<_, _>> assignable to ReadonlyMap<_, _>.