Cache of a single regmatch_t to prevent many calls to malloc

Property definitions

core $ Regex :: native_match
	# Cache of a single `regmatch_t` to prevent many calls to `malloc`
	private var native_match: NativeMatchArray is lazy do
		native_match_is_init = true
		return new NativeMatchArray.malloc(native.as(not null).re_nsub+1)
	end
lib/core/re.nit:183,2--187,4