Re: [boost] Interest in StaticVector - fixed capacity vector

Subject: Re: [boost] Interest in StaticVector - fixed capacity vector
From: Christian Holmquist (c.holmquist_at_[hidden])
Date: 2011-10-12 18:36:12

On 12 October 2011 12:30, Nathan Ridge <zeratul976_at_[hidden]> wrote:

>
> > > I'm presently against any throwing behavior related to resizing of a
> > > StaticVector/static_vector, since one can usually easily check the
> relevant
> > > preconditions themselves.  Just assert.  For those who want defined
> > > behavior
> > >
> > It's not always you know that you're dealing with a static_vector, but
> just
> > some code that expects push_back() to work or throw.
>
> Consider a generic algorithm that takes a "push_back-able" type and inserts
> elements into it using push_back(), and expects the push_back() to work to
> throw.
>
> When you invoke this algorithm, you either know in advance how
> many elements it will add, or you don't.
>
> If you do, then when calling this algorithm *with a static_vector*, you
> need
> to check beforehand whether there is enough space in the static_vector.
> I think that's a reasonable requirement, given that you know, at the call
> site,
> that you're dealing with a static_vector.
>
> If you don't, then calling the algorithm with a static_vector is a
> conceptual
> error in the first place, because you are passing a container with a fixed
> capacity to an algorithm that expects to be able to add a variable number
> of elements to it.
>
>
I realize the validity of your point, and I don't disagree in general.
But I often look through the eyes of code maintenance for very large
projects, and if
I encounter a line like:
m_Somethings.push_back(...);
I don't consider that a possible source of undefined behaviour.
It's too easy for a maintenance programmer to add another line exactly the
same, without realizing he's broken the preconditions.

If that code would read
m_Somethings.unchecked_push_back(...) it's at least less likely that someone
would add another such line without further investigation.

Either way, some people want an unchecked version and others want a checked
version, both are useful, admittedly.. Question is if we should have
1) push_back() & unchecked_push_back()
or
2) push_back() & checked_push_back().

- christian