On Wednesday, September 6, 2017 at 4:03:40 PM UTC+5:30, ROGER GRAYDON CHRISTMAN
wrote:
> On 5 Sep 2017 14:28:44, (Dennis Lee Bier) wrote:
> > On 5 Sep 2017 17:57:18 GMT, <a onclick="addTo('ram')"
>
> >> But what does "a C++ reference" refer to?
> >>
>
> > Per Stroustrup (The C++ Programming Language 4th Ed, page 189)
>
> > """
> > * ...> * A reference always refers to the object to which it was
> > initialized.
> > * ...
>
> > A reference is an alternative name for an object, an alias. ...
> > """
>
> > {Hmmm, and I see that the syntax can be used outside of parameter
> > declaration -- which is the only place I'd seen it previously... either
> > this is a change from earlier standards, or my classes just didn't feel the
> > need to expose a non-parameter reference -- since, based upon the above
> > book, you can not declare a bare reference "variable"; it MUST be
> > initialized with a real object.}
>
> I think I can say something about this, having been a teacherof the classes
> you refer to. I intentionally avoided reference variables.
> IMO, the 'good' use for declaring a new reference variable (i.e. not
> parameter)would be when (1) the object to which you refer to is
> time-consuming to access(2) you plan to refer to this object more then once,
> and don't want to repeatthat time-consuming process, and (3) you really want
> a reference, and not a copy.
> The first two years of programming courses really do not have a purposethat
> meets all three, so can "didn't feel the need" is probably applicable.
> I intentionally avoided them because reference variables simply compoundthe
> problem of aliasing, so unless you really limit your reference variableto a
> very tight sandbox, you could be causing more headache than you save.
> I do admit to occasionally defining a method that returned a reference,such
> as one that overloads the [] operator. But even so, I would generallybe
> reluctant to giving an outside client a direct access to my
> database'sinternal structures. (Thank you Python for separating __getitem__
> and __setitem__)
> Python doesn't eliminate aliasing, of course, since most assignment
> operationscreate aliases. But at least it's nice to know that aliasing
> immutable valuesis harmless. Hence my unit on building recursive data
> structures entirelyout of tuples.
The realization that immutability is a significant virtue is now beginning
to percolate mainstream programming
Ive seen it in recent C# books as a definite recommendation… Something like
- Use value types
- Use getters but no setters
And you have a good design
Python makes this hard by giving less status to immutable types than mutable
ones
- set comprehensions exist not frozenset comprehensions
- Likewise tuples and lists
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