perf(serde_v8): preallocate vector when serializing arrays (denoland#…

…9955)

serde_v8/src/ser.rs

@@ -103,13 +103,12 @@ pub struct ArraySerializer<'a, 'b, 'c> {
 }
 
 impl<'a, 'b, 'c> ArraySerializer<'a, 'b, 'c> {
- pub fn new(scope: ScopePtr<'a, 'b, 'c>) -> Self {
- // let serializer = Serializer::new(scope);
- Self {
- scope,
- // serializer,
- pending: vec![],
- }
+ pub fn new(scope: ScopePtr<'a, 'b, 'c>, len: Option<usize>) -> Self {
+ let pending = match len {
+ Some(len) => Vec::with_capacity(len),
+ None => vec![],
+ };
+ Self { scope, pending }
  }
 }
 
@@ -421,8 +420,8 @@ impl<'a, 'b, 'c> ser::Serializer for Serializer<'a, 'b, 'c> {
  }
 
  /// Serialises any Rust iterable into a JS Array
- fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
- Ok(ArraySerializer::new(self.scope))
+ fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
+ Ok(ArraySerializer::new(self.scope, len))
  }
 
  fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {