[Cthulhu_]

I think it's easy to assume that in this case Go's regex library would keep an internal cache of expressions, using the expression string as a map key. But on the other, I can see why they haven't implemented it, because it obscures memory usage from direct control of the author.

It would probably be a good idea to add performance hints like 'prefer to put static regular expressions in a package variable' in a linter or go vet.

[_ph_]

Actually I would expect any package not to silently cache things until explicitly specified. This otherwise creates an unbounded memory leak.

Moving static (at least as much it concerns the loop) expressions out of a loop is one of the most fundamental optimizations a programmer should do when writing code.

[shakow]

> I think it's easy to assume that in this case Go's regex library would keep an internal cache of expressions

IMHO, the stdlib doing implicit memoization is a catastrophe waiting to happen.

I think that handling regexps and caching functions are two composable and orthogonal features that should be handled by two packages/libs/... .