Re: [PATCH] refactor Vector

On 02/02/2014 02:42 PM, Amos Jeffries wrote:

> in src/HttpHdrRange.cc
>
> * This pattern happens several times throughout this patch:
> - while (!specs.empty())
> - delete specs.pop_back();
> + while (!specs.empty()) {
> + delete specs.back();
> + specs.pop_back();
> + }
>
> ** std::vector::pop_back() is documented as erasing the element.
> Squid::Vector does not.
> - under correct usage of std::vector the loop and delete X.back() would
> seem to be irrelevant.
>
> ** the pattern with loop seems to be equivalent to specs.clear() but far
> less efficient. Efficiency is saved here only by Squid::Vector not
> reallocating the items array in pop_back().

An explicit delete is necessary when storing raw pointers to objects.
Neither std::vector nor Squid's Vector [can] delete objects that
elements removed by clear() or pop_back() point to.

A generic container does not know whether it stores "raw pointers to
objects" or "just objects". When removing elements, it has to use the
element's default constructor or destructor. When an element is a raw
pointer, the default constructor and destructor do not do anything
[useful], so we have to delete those objects by hand using "delete" (or
use smart pointers instead).

One could avoid the explicit loop using std::for_each. However, it would
not make things more efficient (or more clear) as far as vector memory
management is concerned.

HTH,

Alex.
Received on Tue Feb 04 2014 - 01:17:33 MST