Easiest way to make tenth(), hundredth(), etc to go alongside first() and second()?

General Usage
1

So first is an extremely useful function, and so is last.

Some languages, like rails, even have a second() function. This has led to some controversy on the subject:

What is the best way to define all the numbers from two to one thousand as functions that grab indices from arrays?

This might help a little?

2

For the record, I think this is a terrible idea and nobody should do it. But, jut for fun

nthlist = ["first", "second", "third", "fourth", "fifth"]

for (n, nth) ∈ enumerate(Symbol.(nthlist))
    isdefined(@__MODULE__, nth) && continue
    @eval $nth(v) = v[$n] 
end

Of course, you’d have to do a little bit of English and string manipulation to generat nthlist. If you can find an existing list you’d be all set. It wouldn’t be hard to extend this to general iterators that don’t support indexing.

Seriously though, don’t do it.

3 Likes
3

Ah, the obviousness of 0-based indexing:

10 Likes
4

Wow, I’ve gotten so used to multiple dispatch that I stared at that code snippet for a few minutes in complete puzzlement before I realized what it meant. This coming from someone with about 8 years of mostly C++.

5

Obviously, you need to start with zeroth!

2 Likes
6

FWIW, coming from Common Lisp I originally missed first, …, tenth, but now I think that

  1. In the (rare) cases I need it, x -> x[n] is more readable and should compile equally efficiently now (for a constant n),
  2. More generally, using accessors like this encourages bad coding habits as it forces the user to remember the layout. This is a reasonable compromise for 2 elements, but for anything more, we have NamedTuples (which are lightweight and yet optimized, ideal for most cases), composite types (for something you use more extensively), Dicts (for a heterogeneous number of elements), etc.