Yeah thats a good point. The use-case I wrote this for involved decoding a protobuf message that has only 3 fields, but where the total size is several MiB. For my workload this optimization is meaningless, the most important thing is to avoid allocating huge slices, but for lots of small protobufs like the one you defined a hand-rolled solution will definitely be faster.

Do you think I could just manually inline the decoding code as much as possible in the molecule library, or does it need a different API?

Also if you open a P.R I'll merge it :)