What do you assume when you see fromListN in a library?

[John Ky]

I expect it to pre-allocate space for N elements and populate the vector
until there are no more elements or the vector is full and return a vector
that has a size the minimum of the length of the input list and N.

To me size hint is definitely not what I want because it hides
performance/allocation bugs.

If it is possible to modify the function type then I would have it return a
tuple of a vector with maximum size N as well as the remainder of the list.

On Fri, 28 Feb 2020, 2:41 pm Zemyla, <zemyla at gmail.com> wrote:

> I'm kind of the opposite. I think the number given to fromListN should be
> a "size hint", not a redundant coding of the size of the list given.
>
> On Thu, Feb 27, 2020, 21:31 chessai . <chessai1996 at gmail.com> wrote:
>
>> I expect a list with precisely length N, and reject anything else. IIRC
>> both primitive and vector do this
>>
>> On Thu, Feb 27, 2020, 6:54 PM Carter Schonwald <
>> carter.schonwald at gmail.com> wrote:
>>
>>> Hey everyone:
>>> When you see fromListN as a function in a library, do you assume /
>>> presume it’s expecting an exactly N element list ? Or do you
>>> expect/tolerate other behavior ?
>>>
>>> Should it reject shorter lists?
>>>
>>> Should it truncate or reject longer lists?
>>>
>>> A corner case of this came up in some bug discussion I was having
>>> regarding vector,  and I shall claim and or presume that most folks assume
>>> exact size with prompt rejection of too long or too short.
>>>
>>> Thoughts please ?
>>>
>>> -Carter
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