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feat(tvix/eval): NixList::concat(): avoid an unnecessary move

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In `a++b`, the previous implementation would move `b` (i.e. memcpy
its elements) twice.  Let's do that only once.

We sure do call NixList.clone() a whole lot.  At some point in the
future we probably want to do a SmolStr-type split for NixList into
a two-variant enum where one side is an Rc<Vec<Value>> for lists
longer than a certain length.

Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: I32154d18785a1f663454a8b9d4afd3e78bffdf9c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7040
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
This commit is contained in:
Adam Joseph 2022-10-18 22:31:30 -07:00 • committed by clbot
parent 4b01e594d5
commit c91d86ee5c
1 changed files with 3 additions and 4 deletions
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7
tvix/eval/src/value/list.rs
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@ -50,10 +50,9 @@ mod arbitrary {
impl NixList { impl NixList {
pub fn concat(&self, other: &Self) -> Self { pub fn concat(&self, other: &Self) -> Self {
let mut lhs = self.clone(); let mut ret = self.clone();
let mut rhs = other.clone(); ret.0.extend_from_slice(&other.0);
lhs.0.append(&mut rhs.0); ret
lhs
} }
pub fn len(&self) -> usize { pub fn len(&self) -> usize {