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authorVincent Ambo <mail@tazj.in>2022-12-29T11·44+0300
committertazjin <tazjin@tvl.su>2022-12-29T12·27+0000
commit5d73c06b1a67bce68dcc0b2bd5f087ce00ab6317 (patch)
tree62d40c8ca8e1620bff028c8d89a5a0f05ee00661 /tvix/eval/src/builtins/mod.rs
parent6ab8320f075e36f2328a86f5fcf7674844a0bd12 (diff)
refactor(tvix/eval): use im::Vector for NixList representation r/5534
This is a persistent, structurally sharing data structure which is
more efficient in some of our use-cases. I have verified the
efficiency improvement using `hyperfine` repeatedly over expressions
on nixpkgs.

Lists are not the most performance-critical structure in Nix (that
would be attribute sets), but we can already see a small (~5-10%)
improvement.

Note that there are a handful of cases where we still go via `Vec`
that need to be fixed, most notable for `builtins.sort` which can not
currently be implemented directly using `im::Vector` because of a
restrictive type bound.

Change-Id: I237cc50cbd7629a046e5a5e4601fbb40355e551d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7670
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Diffstat (limited to 'tvix/eval/src/builtins/mod.rs')
-rw-r--r--tvix/eval/src/builtins/mod.rs7
1 files changed, 6 insertions, 1 deletions
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 3c635eb364ca..709d2918f3c0 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -772,7 +772,12 @@ mod pure_builtins {
 
     #[builtin("sort")]
     fn builtin_sort(vm: &mut VM, comparator: Value, list: Value) -> Result<Value, ErrorKind> {
-        let mut list = list.to_list()?.into_vec();
+        // TODO: the bound on the sort function in
+        // `im::Vector::sort_by` is `Fn(...)`, which means that we can
+        // not use the mutable VM inside of its closure, hence the
+        // dance via `Vec`. I think this is just an unnecessarily
+        // restrictive bound in `im`, not a functional requirement.
+        let mut list = list.to_list()?.into_iter().collect::<Vec<_>>();
 
         // Used to let errors "escape" from the sorting closure. If anything
         // ends up setting an error, it is returned from this function.