Thanks, I already looked at the source 
I was talking about confirming whether or not the existing rehash! would already work for the purpose of shrinking the Dict. The relevant parts of the code (both of rehash! as well as sizehint!) hasn’t changed in the last 9 years and the todo comment is still there, so I’d rather err on the side of caution and say jeff had a failure mode in mind when writing that code. Exhaustively checking all possible usages of dict shrinking isn’t feasible though…