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Why "splice"

Rope splices from the Nordisk familjebok, a long splice on the left

Rope splices, a) a long splice, from the Nordisk familjebok, 2nd edition, vol. 26 (1917). Public domain, via Wikimedia Commons.

A splice joins two things into one: ropes, film, tape, wires, optical fibres, wooden beams, genes. The name git-splice borrows from all of them.

Rope splicing​

A long splice unlays the strands of two ropes and weaves each into the other. Unlike a knot, or even a short splice, it adds no lump: the joint has nearly the rope's own diameter and runs through a pulley like the rest of the rope.

git-splice works the same way. The upstream's files are woven into the monorepo as an ordinary folder, with no submodule pointer (gitlink) and nothing extra to check out. You see the joint only as one small file, <path>/.splice, which records the upstream.

Noun and verb​

As a noun, a splice is the joint: here, the folder together with its connection to the upstream repository. "The vendor/a/ splice" is the folder vendor/a/ and the upstream it syncs with.

As a verb, you splice something in or out:

  • splice in: bring upstream content into the monorepo, with clone, merge and pull.
  • splice out: publish the monorepo's changes upstream, with push.

The vocabulary defines these and the other terms.

RNA splicing​

In RNA splicing, a cell cuts the introns out of a gene's transcript and joins the remaining exons into one continuous strand.

push does something similar to the monorepo's history. A monorepo commit may touch the splice and app/ at once. The rebuild keeps only the part inside the folder, drops commits that don't touch it, and joins the rest into a history the upstream can take as its own.

Array.prototype.splice​

JavaScript's splice removes and inserts elements in place: unlike slice, it changes the array it is called on.

const files = ["app", "lib", "docs"];
files.splice(1, 1, "lib v2");  // files is now ["app", "lib v2", "docs"]

git-splice changes the repository it runs in, too. pull merges the upstream's changes into the folder in place, as an ordinary commit on your branch, rather than checking them out somewhere else.