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

There are at least two reasonable sorts of hint: upper bounds and lower bounds. For arrays, either can be useful, but upper bounds are especially nice in combination with resizing primitives (currently only available for SmallArray and ByteArray-backed arrays). For sequences, lower bounds are useful, but upper bounds aren't really. On Fri, Feb 28, 2020, 1:49 PM Oleg Grenrus wrote:

My personal expectations may be different based on what the container in question is. Elsewhere in the discussion types in `primitive` and `vector` were mentioned. They are however different.

Compare to C++ code snippets, which are all morally `fromList(N)`:

std::array variantA; for (int i = 0; i < 100; i++) { primitive[i] = f(i); }

// not good std::vector<int> variantB; for (int i = 0; i < 100; i++) { primitive.push_back(f(i)); }

std::vector<int> variantC; variantC.reserve(100); for (int i = 0; i < 100; i++) { primitive.push_back(f(i)); }

I'm not a fan of changing `fromListN` to be partial function, but if that change is carried on in `vector` there should be a variant which allows to `reserve` without worrying about partiality.

- Oleg

On 28.2.2020 4.53, Carter Schonwald 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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