Optimize From<Vec<T>> for EcoVec<T>

[bergkvist]

Inspired by the implementation of From<Vec<T>> for Arc<[T]>:
https://github.com/rust-lang/rust/blob/175e04331be56c5b4bdf77478434b1a5e0556770/library/alloc/src/sync.rs#L3823-L3851

• Vec::into_raw_parts(self) APIs are experimental, so we can't use them, even though the stdlib Arc implementation uses it internally.

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When we copy/move the elements from the Vec into the EcoVec, we need to ensure that the items don't get dropped twice.

• For this we use Vec::set_len(&mut self, len: usize) to set the length to 0, which ensures that when the Vec is dropped later, and its buffer is freed - it doesn't run drop on the individual items that were moved into the EcoVec.

[laurmaedje]

Thanks!

[laurmaedje]

Published ecow 0.2.6 with this change.