Making format machinery more amenable to dynamic formatting

[birkenfeld]

@djc

Another alternative (which is probably unattractive for you and your immediate problem, but nonetheless): spend some designing a comprehensive V2 to replace V1, which is amenable for making public & stabilization.

There was a thread a while ago awhile ago about speeding up formatting with a new behind-the-scenes implementation:

Changing core::fmt for speed

The current machinery in core::fmt is built in a way that any expansion of format!/write!/etc keeps most of the code out of the call site, and inside core::fmt::write(). To do this, it has to pass an array of arguments, and since the arguments may be different types, it uses (sort-of-but-different) trait objects to do so. This results in formatting to be noticeably slower than pushing values to a string manually. After some rusty archaeology, the best I could find was this issue, stating: It …