Re: Proper use of templated containers as class members
On Dec 7, 7:47 pm, Jeff Schwab <j...@schwabcenter.com> wrote:
James Kanze wrote:
On Dec 5, 8:31 pm, Jeff Schwab <j...@schwabcenter.com> wrote:
Victor Bazarov wrote:
James Kanze wrote:
If you return a reference, it can only be to a "contained
object". Otherwise, how do you manage its lifetime.
...
And even if it is part of the object, the idea behind the
typedef combined with the accessor essentially represents
the abstraction which should tell the user of the class
*not* to rely on what the typedef resolves to.
As concrete examples, there are standard library instance
methods that return char const*, but do not necessarily
store instance data in contiguous, null-terminated arrays.
std::string::c_str() comes to mind.
Really. Do you know of an implementation of std::string
which doesn't store the data in contiguous, null-terminated
arrays?
Sure. The first GCC I used, 2.95, only added a terminating
null when an API call made it necessary. No implementation I
know of stores the array in the simple-minded way you're
implying; e.g., CoW implementations often share one array
among multiple string instances. The only case I can think of
in which a c_str really is just returning a pointer-to-member
is when the Small String Optimization has been applied, but
even that pointer could be invalidated by subsequent appends
to the string.
Which is all really irrelevant to the point at hand. The
function c_str returns (or returned) a pointer to the internal
representation of the string in all of these cases, and the next
version of the standard will require it. (There is some
argument that the current version unintentionally requires it as
well.)
[...]
The debate was whether the typedef implies the implementation.
You argued that it did, partially because the OP's accessor
method returned a reference.
I argued that the posted code would expose the implementation,
because it returned a reference. The typedef has nothing to do
with it, except in the case where it is used in place of a
member class or something similar. Nobody's arguing against
typedef; the argument was against exposing the type at the
interface level.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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