Re: C++0x container constructors for DefaultConstructible objects - no allocator?

From:

bop@gmb.dk ("Bo Persson")

Newsgroups:

comp.std.c++

Date:

Mon, 21 May 2007 22:44:14 GMT

Message-ID:

<5bel29F2s4c3gU1@mid.individual.net>

Howard Hinnant wrote:
:: In article <5b91g3F2rt1iiU1@mid.individual.net>,
:: bop@gmb.dk ("Bo Persson") wrote:
::
::: I notice in the draft N2284 that sequence containers have had one
::: constructor split in two. We now have (for list<T>):
:::
::: explicit list(size_type n);
::: list(size_type n, const T& value, const Allocator& = Allocator());
:::
::: How come the first type of constructor doesn't take an allocator
::: parameter?
::
:: Mainly just history. People have never been able to say:
::
:: std::list<T, A> c(n, A());
::
:: And I've never heard any requests for that functionality. So I
:: didn't add it. It easily could be added. Is there demand for it?
:: Would you be willing to write a short paper or defect report with
:: detailed proposed wording relative to N2284?
::

I was really just curious about why one constructor breaks the
pattern. Having already written a defect report for for strings
(#614), I noticed that other containers now also deviate from the
container requirements in 23.1/9, where it says that constructors
should all take an Allocator& argument. Except when they don't?

I can also guess that the new constructor should default construct the
container's allocator member, but haven't found that it says so
anywhere. Did I miss this requirement, or is it just obvious anyway?

Bo Persson

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