[Issue 16457] std.regex postprocesses ctRegex every time at runtime

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16457

--- Comment #2 from greenify <greeenify at gmail.com> ---
thanks a lot for looking at this so quickly :)

> The problem is enum re = ... line. Enum means ctRegex!`((c)(s)?)?ti` is copy-pasted at the place of usage, basically reconstructing regex on each loop iteration b/c compile-time version can't cache compiled patterns.

Okay that makes partially sense, but to give some background I found this
problem because the D changelog generation crashed on my machine (16G) while
parsing a 300kB log file. The dummy file is a dustmited & reduced version of
the changelog generator:

https://github.com/dlang/tools/blob/master/changed.d#L77

And using `enum ... = ctRegex!...` seems to be a very common pattern:

https://github.com/search?q=enum+ctRegex&type=Code&utf8=%E2%9C%93

> Replace enum with static and all should be good.

Unfortunately I can still observe the same behavior, I also tried to move
ctRegex to the matchAll.
Funnily with regex I don't get this allocation / out of memory -problem.

FYI static immutable doens't work:

foo.d(10): Error: template std.regex.matchAll cannot deduce function from
argument types !()(string, immutable(StaticRegex!char)), candidates are:
/usr/include/dlang/dmd/std/regex/package.d(860):        std.regex.matchAll(R,
RegEx)(R input, RegEx re) if (isSomeString!R && is(RegEx ==
Regex!(BasicElementOf!R)))
/usr/include/dlang/dmd/std/regex/package.d(868):        std.regex.matchAll(R,
String)(R input, String re) if (isSomeString!R && isSomeString!String)
/usr/include/dlang/dmd/std/regex/package.d(875):        std.regex.matchAll(R,
RegEx)(R input, RegEx re) if (isSomeString!R && is(RegEx ==
StaticRegex!(BasicElementOf!R)))

--