prealloc size of Lower::lower_into_rust_buffer #2420
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bendk
requested changes
Jan 29, 2025
| @@ -245,7 +245,7 @@ pub unsafe trait Lower<UT>: Sized { | |||
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| /// Convenience method | |||
| fn lower_into_rust_buffer(obj: Self) -> RustBuffer { | |||
| let mut buf = ::std::vec::Vec::new(); | |||
| let mut buf = ::std::vec::Vec::with_capacity(size_of::<Self>()); | |||
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This would be a great optimization, but is size_of<Self> the right value? Our serialization code and Rust's type layout are very different. Still, maybe size_of<Self> is a good estimate -- I'm not really sure.
Can you do some tests? Like create a set of Records, Enums, strings, vecs and hashmaps, some with few fields/variants/items, some with lots of them, then compare size_of::<Self> against lower_into_rust_buffer(self).len(). I'd love to see the results of that.
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