GrowableArray currently supports setting an initial capacity at construction time, and querying the current capacity via max_length(). It does not support functions like reserve and shrink_to_fit provided by std::vector. It's possible to work around that lack, but requires some non-trivial effort. (See StringDedupTable for example.) We should add those functions. those functions. While we're at it, rename max_len to capacity, for consistency with std::vector and to aid discovery by someone familiar with that class.