[karmakaze]

The way to fix it in that manner here is to undo the 42% speedup and return the heap allocated object for the caller to mangle.

[account42]

Yes, if you are serious about backwards compat then you pay that cost and perhaps add a separate function that is faster for callers to opt into.

[karmakaze]

Effectively deprecating the old one and recommending the new one being a way to smoothly 'fix' an API.