Should indexing wrap?

[jonathanhogg]

There is an argument that indexing should wrap the same way that vector expansion in operators works, i.e., indices are modulo the length of the vector.

This would have a few benefits:

• Places where I currently expand a vector manually out to a particular length to ensure indexing works (e.g., multiplying sizes by (1;1;1)) would just work
• Negative indexing could be used to select from the other end of a vector without having to call len() and do a subtraction
• A single number could be easily expanded out to an arbitrary length vector with slicing, e.g., 5[..100] would produce a hundred long vector all consisting of the number 5

Question: should multi-binding let statements also wrap a short vector or should they match the behaviour of a multi-binding for loop? It would seem to be useful if they did wrap, as then one could write:

let width;height=SIZE

and have it do The Right Thing without having to do SIZE * (1;1).

This feels like it would be a substantive enough change that I should do it before 1.0.0 or not do it at all.

[jonathanhogg]

A possible down-side of this might be if I slice a vector anywhere and expect that a short vector will be honoured.

Seems like the best idea is to try this in a branch and test all of my existing code to see if any breaks…

[jonathanhogg]

Note that indexing null is still going to have to return null.

[jonathanhogg]

Initial tests with draft PR show that it seems to work fine.

[jonathanhogg]

Actually, on that "expanding out a vector note", you could force any vector to be a specific size with a range. So if radius needs to be 3 items long, then a simple radius[..3] would accomplish that. Most of the time this wouldn't be necessary, but it'd be handy when using functions like hypot(). So hypot(SIZE[..2]) would give the diagonal length of a SIZE rectangle even if SIZE is a single value (i.e., a square).