scovich commented on code in PR #7922:
URL: https://github.com/apache/arrow-rs/pull/7922#discussion_r2207963894
##########
parquet-variant/src/builder.rs:
##########
@@ -402,6 +402,11 @@ impl<S: AsRef<str>> FromIterator<S> for MetadataBuilder {
impl<S: AsRef<str>> Extend<S> for MetadataBuilder {
fn extend<T: IntoIterator<Item = S>>(&mut self, iter: T) {
+ let iter = iter.into_iter();
+ let (min, max) = iter.size_hint();
+
+ self.field_names.reserve(max.unwrap_or(min));
+
for field_name in iter {
self.upsert_field_name(field_name.as_ref());
Review Comment:
> I agree in theory it is not a great idea
>
> However in practice I think it is common to reserve capacity (allocate)
based on the size hint and it is done several other places in this crate
I was referring specifically to the _upper_ bound. All the code you link
(**) only looks at the _lower_ bound, which is a lot less dangerous.
(**) except [`FromIterator for
BooleanArray`](https://github.com/apache/arrow-rs/blob/a2cc42639b4ad5579d052e6f2317a413e2407e0f/arrow-array/src/array/boolean_array.rs#L435-L434),
for some reason.
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