[Proposal] Apply copy-on-write (COW) rule wherever possible

[pwwang]

Only copy the data when possible. For example:

df = mutate(mtcars)

# currently, df is a copy of mtcars
# but if there are no changes made to mtcars, it should be:
# df is mtcars

[machow]

Hey--I suspect that copying ends up being pretty cheap computationally and space-wise. AFAIK a lot of the internal references are preserved (e.g. to underlying "Blocks" / arrays), until there's something that would mutate them.

(I could definitely be wrong here though)

[pwwang]

Thanks for pointing this out. I somehow agree with you. This is a low priority as this could anyway save resources.