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symmetric difference operation for sets via xor (#24286)

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closes https://github.com/nim-lang/RFCs/issues/554

Adds a symmetric difference operation to the language bitset type. This
maps to a simple `xor` operation on the backend and thus is likely
faster than the current alternatives, namely `(a - b) + (b - a)` or `a +
b - a * b`. The compiler VM implementation of bitsets already
implemented this via `symdiffSets` but it was never used.

The standalone binary operation is added to `setutils`, named
`symmetricDifference` in line with [hash
sets](https://nim-lang.org/docs/sets.html#symmetricDifference%2CHashSet%5BA%5D%2CHashSet%5BA%5D).
An operator version `-+-` and an in-place version like `toggle` as
described in the RFC are also added, implemented as trivial sugar.
This commit is contained in:
metagn
2024-10-19 11:07:00 +03:00
committed by GitHub
parent 0a058a6b8f
commit ae9287c4f3
12 changed files with 85 additions and 7 deletions
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20
tests/stdlib/tsetutils.nim
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@@ -44,6 +44,26 @@ template main =
s[a2] = true
s[a3] = true
doAssert s == {a2, a3}
block: # set symmetric difference (xor), https://github.com/nim-lang/RFCs/issues/554
type T = set[range[0..15]]
let x: T = {1, 4, 5, 8, 9}
let y: T = {0, 2..6, 9}
let res = symmetricDifference(x, y)
doAssert res == {0, 1, 2, 3, 6, 8}
doAssert res == (x + y - x * y)
doAssert res == ((x - y) + (y - x))
var z = x
doAssert z == {1, 4, 5, 8, 9}
doAssert z == x
z.toggle(y)
doAssert z == res
z.toggle(y)
doAssert z == x
z.toggle({1, 5})
doAssert z == {4, 8, 9}
z.toggle({3, 8})
doAssert z == {3, 4, 9}
main()
static: main()