mergeDeepLeft behaves differently than in @types/ramda about types HOT 4 CLOSED

Not done intentionally. ts-toolbelt is used under the hood for types like this, and a Major version bump of that library happened with the migration over to types-ramda.

This behavior still works as expected

type Foobar = { foo: { bar: string } };

const obj1: Foobar = { foo: { bar: 'hello' } };
const obj2: Foobar = { foo: { bar: 'world' } };

const r: Foobar = mergeDeepLeft(obj1, obj2);

While not ideal, you can get around your issue by doing as unknown as T

function merge<T extends { lang: string }>(arr: T[]) {
  return mergeDeepLeft(arr[0], arr[1]) as unknown as T;
}

See this typescript playground for more details: https://tsplay.dev/mA8zQN

Will look into it is worth wrapping our own for this instead of relying on ts-toolbelt

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While not ideal, you can get around your issue by doing as unknown as T

That's what I ended up doing, thanks for the elaborate answer :).

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@sandrosc while investigating how to fix this, I found quite a bit wrong with O.Assign for both shallow and deep merges. I took a crack at fixing them and found myself writing my own types to replace O.Assign

It does fix your specific issue, check out the MR: #18

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I took a look at the new types, looks great. Didn't know the 1/0 pattern for if/else, learnt something new :).

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