> But that's only run when the pool needs to allocate more space. What GP seems to expect is that sync.Pool() would always return a zeroed structure, just as Go

> But that's only run when the pool needs to allocate more space. What GP seems to expect is that sync.Pool() would always return a zeroed structure, just as Golang allocation does. Not quite that. Imagine I have a pool of buffers with a length and capacity, say when writing code to handle receiving data from the network. When I put one of those buffers back, I would like the next user of that buffer to get it back emptied. The capacity should stay the same, but the length should be zero. I think it’s reasonable to have a callback to do this. One, it doesn’t force every consumer of the pool to have to remember themselves; it’s now a guarantee of the system itself. Two, it’s not much work but it does prevent me from re-emptying freshly-allocated items (in this case reinitialzing is fast, but in some cases it may not be). This also should be an optional callback since there are many cases where you don’t want any form of object reset.