Do we really need CowMut Enum?

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CowMut enum is in file cow_mut.rs and is mainly used by GreenNodeBuilder to deal with the differences of owning NodeCache or mutable reference of NodeCache. I wonder whether using trait BorrowMut is better? As trait has no runtime overhead than enum?

[bjorn3]

GreenNodeBuilder starts with a borrowed CowMut and may or may not replace it with an owned CowMut in the future. Using BorrowMut doesn't work for this as you have to commit to either a borrowed or owned value in advance.

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GreenNodeBuilder starts with a borrowed CowMut and may or may not replace it with an owned CowMut in the future. Using BorrowMut doesn't work for this as you have to commit to either a borrowed or owned value in advance.

What's the meaning of "borrowed" or "owned"? Is it state of the CowMut enum?

I'm not very sure. But I did not find any state changes in CowMut and the usage in GreenNodeBuilder. It seems like that the lifetime and the state of CowMut(cache) is stabelized when GreenNodeBuilder was first created.

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And I think even replace CowMut with BorrowMut does not change the future plan of "GreenNodeBuilder starts with a borrowed CowMut and may or may not replace it with an owned CowMut". As the change of the state of cache(CowMut) would reflect on the lifetime of GreenNodeBuilder?

Finally, thanks for explaining the considerations of the design. I just find it hard to capture the design of the CowMut.

[bjorn3]

I'm not very sure. But I did not find any state changes in CowMut and the usage in GreenNodeBuilder. It seems like that the lifetime and the state of CowMut(cache) is stabelized when GreenNodeBuilder was first created.

Looks like that is indeed the case.