std/iteration/concatenate
std/iteration/src/concatenate.trb
One step, and the reason the whole package needs it: putting many short texts together into one long one.
It is here and not in std/text because std/text depends on this package and not the other way round, and because
both places that join a text - Iterate.joined and the joining collector - are words of this package.
fn concatenated
fn concatenated(pieces: List<String>, separator: String): StringThe pieces in one text, with separator between every two of them. This is what Iterate.joined is, and the way to
build a long text out of many short ones.
Reach for it instead of appending in a loop. A String is a value, so appending to one copies everything that is
already in it: n appends copy O(n²) bytes, and for the 66 megabytes of C the compiler writes about itself that is
hours of copying. This merges neighbours pairwise instead, so every byte is copied once per level of the merge tree
and there are log n levels - a fraction of a second for the same text. What comes out is the same either way: a tree
over n leaves has n - 1 forks, and each fork writes one separator.
Examples
print concatenated(["a", "b", "c"], ", ")
print concatenated([], ", ")
Pitfalls
It holds the pieces and one merged level at the same time, so the peak is about twice the result. A caller that has to stay inside a fixed budget writes the pieces out one at a time instead of building the whole text at all.