How to merge tuples together? I need to add one tuple after end of another like below.
type MergeTuple<A extends any[], B extends any[]> = [...A, ...B];
Only thing that works is this:
type MergeTuple<A extends any[], B extends any[]> = [A[0], B[0]];
But that works with static count of items
MergeTuple<['a'], ['b']> // is ['a', 'b']
Not working for this
MergeTuple<['a', 'b'], ['c']> // is ['a', 'c'] expected ['a', 'b', 'c']
Concatenating Tuples in TS is currently just possible with very ugly workarounds.
Here is how one library does it
You don't want to do that yourself. Ask yourself if you really need that, and if the answer is yes, do yourself the favor and use a type library like typescript-tuple.
Does this not work for you?
type MergeTuples<
A extends readonly any[],
B extends readonly any[]
> = [...A, ...B];
Here is a playground if needed.
If you can get your multiple tuple fragments into array form, then you can also use a type like this for an arbitrary amount of tuple fragments:
type Flattened<Fragments extends any[][]> =
Fragments extends
[
infer CurrentTupleFragment extends any[],
...infer RemainingTupleFragments extends any[][]
] ?
[
...CurrentTupleFragment,
...Flattened<RemainingTupleFragments>
] :
[];
type flat = Flattened<[["a", "b"], ["c"], ["d", "e", "f"]>; //["a", "b", "c", "d", "e", "f"]
This works its magic by first recursively splitting the array into its front element CurrentTupleFragment and the remaining yet to be recursively treated elements until it hits the end of the array (the first extends clause does not match anymore) and then returning an empty array up the recursion chain.
When on the way back up, we then spread out the CurrentTupleFragment and effectively prepend them to the already spread out tuple fragments from our recursion, which we of course need to spread out again, otherwise we would get ever deeper nested Arrays (try removing the ... before the recursive Flatten to see what I mean).
