setSize may only downsize

[sumeetsgh93]

While using this library with immutable-js, we are encountering a typedError "setSize may only downsize".
But there could be cases in which list size might increase. Why there is this restriction of downsize?

[davecoates]

I'm assuming this was done as if you increase the size the elements would only be valid if they were a Maybe type, eg. if you had a List(Number) and you increase it's size then all new elements would be undefined as so not be valid numbers.

[sumeetsgh93]

Thanks for quick response.
So in function function mergeIntoListWith(list, merger, iterables) {
var iters = [];
var maxSize = 0;
for (var ii = 0; ii < iterables.length; ii++) {
var value = iterables[ii];
var iter = IndexedIterable(value);
if (iter.size > maxSize) {
maxSize = iter.size;
}
if (!isIterable(value)) {
iter = iter.map(v => fromJS(v));
}
iters.push(iter);
}
if (maxSize > list.size) {
list = list.setSize(maxSize);
}
return mergeIntoCollectionWith(list, merger, iters);
}

setSize is called to increase the size of the list (immutable-js).

But in typed-immutable setSize is restricting upsize.
setSize(size) {
if (size > this.size) {
throw TypeError(setSize may only downsize)
}

return change(this, store => store.setSize(size))

}

I am a bit confused on how both are supposed to work together.

[davecoates]

Ah - so this is when you attempt to merge two lists?

I think we will have to implement a custom merge function on List to handle this

[sumeetsgh93]

Any rough timeline for this? We are facing issues because of this. Obviously, we will do some workarounds for now.