Why not create nodes by List.map?

[Martin521]

The documentation warns against using List.map to create a list of Nodes and recommends forEach instead. Why is this? As far as I can see, forEach creates the list in a way that does not differ from how List.map would do it.
(I do understand the need for using cond, inserting an empty node instead of just dropping a node.)

[Tarmil]

It's a bit complicated, but it's due to the way Blazor's rendering algorithm works. In short, each insertion is associated with a sequence number. These numbers must be consistent between two consecutive renders for the algorithm to work. If you insert items using something like List.map, then as soon as the list has changed length between two consecutive renders, the sequence numbers will be inconsistent. forEach fixes the issue by wrapping the content in a RenderFragment with a sequence that resets for each item.

[Martin521]

Thank you for the fast reply. It seems then that in my case (lists of constant length) I can ignore it.
(Perhaps the documentation should say "... rendering collections of unknown length using a function such as ...".)
BTW Bolero is really great, thanks for creating and sharing it.

[akhansari]

Related question:
Does it make sense a helper like this in order to have the index?

let forEachi (items: 'T list) (mkNode: int32 -> 'T -> Node) : Node =
    forEach {0..items.Length-1} (fun i -> mkNode i items.[i])

[Tarmil]

@akhansari It makes sense, although this implementation is not really optimal, because items.[i] on a list needs to go through the list to find the item. I would suggest something like this instead:

let forEachi items mkNode =
    forEach (Seq.mapi mkNode items) id