Strip the versioner's prefixes with each instead of reduce

[ericproulx]

Versioner::Path#before runs on every request of a versioned API and takes the mount path and prefix off the front of PATH_INFO before looking for a version segment:

path_info = @prefixes.reduce(path_info) do |pi, path|
  pi.start_with?(path) ? pi.delete_prefix(path) : pi
end

@prefixes holds at most two entries — a mount path and a prefix — and for an API with neither it is empty. Array does not override Enumerable#reduce, so that list pays the generic accumulator path on every request, which costs more than the work it is driving. In a stackprof run it was 30% of before.

each over the same list, assigning as it goes, is the same operation without it.

Measurements

Same-process A/B on the operation:

@prefixes	reduce	each
one prefix	205 ns	89 ns	2.31x
empty	102 ns	25 ns	4.02x

It allocates less too, which the timing alone does not show — 3 objects against 1 for identical work, the extra two being Enumerable machinery rather than anything the stripping needs:

reduce  3.0 objects
each    1.0 objects

End to end, median of 9 runs interleaved with master's, Ruby 4.0.5 + YJIT:

	master	this branch		objects/req
small path-versioned API	166,376	170,079	+2.2%	36.1 → 34.1

An API that declares no version never builds this middleware and is untouched.

Behaviour

Identical: the same prefixes are removed, in the same order, under the same start_with? guard. each returns the receiver rather than the accumulator, so the stripped value is assigned to the local as it goes.

Touches the same file as #2880, but a different method (before vs version_from_first_segment) — they merge cleanly in either order.

🤖 Generated with Claude Code

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