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Posted by Jerry Stuckle on 09/25/07 10:43
Steve wrote:
> "Jerry Stuckle" <jstucklex@attglobal.net> wrote in message
> news:VLWdnbBpwNDwzmXbnZ2dnUVZ_gmdnZ2d@comcast.com...
>> Shelly wrote:
>>> "Jerry Stuckle" <jstucklex@attglobal.net> wrote in message
>>> news:J_ednRJzLNIw3GXbnZ2dnUVZ_hGdnZ2d@comcast.com...
>>>> Shelly wrote:
>>>>> "gosha bine" <stereofrog@gmail.com> wrote in message
>>>>> news:46f823bf$0$31121$6e1ede2f@read.cnntp.org...
>>>>>> Shelly wrote:
>>>>>>> "Steve" <no.one@example.com> wrote in message
>>>>>>> news:r6VJi.36$Nr6.32@newsfe05.lga...
>>>>>>>> "Joe" <joe@faceh.com> wrote in message
>>>>>>>> news:1190663828.772978.15800@22g2000hsm.googlegroups.com...
>>>>>>>>> I am just starting to use Object Oriented PHP coding, and I am
>>>>>>>>> seeing
>>>>>>>>> quite often the following (this example taken from a wiki):
>>>>>>>>>
>>>>>>>>> $wakka =& new Wakka($wakkaConfig);
>>>>>>>>>
>>>>>>>>> What exactly is the =&, and why is it different from = ?
>>>>>>>> well, better syntax would have helped. it should read ' $something =
>>>>>>>> &$variable'. in this context, & means 'a reference to the memory
>>>>>>>> location where the value is stored'. without the &, it means 'a copy
>>>>>>>> of the value of the variable'.
>>>>>>>>
>>>>>>>> clear as mud? rather than explain memory, let me have you do this:
>>>>>>>>
>>>>>>>> $variable = 'hello';
>>>>>>>> $reference = &$variable;
>>>>>>>> $variable = 'world';
>>>>>>>> echo '<pre>' . print_r($reference, true) . '</pre>';
>>>>>>>> $reference = 'good-bye';
>>>>>>>> echo '<pre>' . print_r($variable, true) . '</pre>';
>>>>>>>>
>>>>>>>> unset($variable);
>>>>>>>> unset($reference);
>>>>>>>>
>>>>>>>> $variable = 'hello';
>>>>>>>> $reference = $variable;
>>>>>>>> $variable = 'world';
>>>>>>>> echo '<pre>' . print_r($reference, true) . '</pre>';
>>>>>>>> $reference = 'good-bye';
>>>>>>>> echo '<pre>' . print_r($variable, true) . '</pre>';
>>>>>>>>
>>>>>>>> the first example, BY REFERENCE, means that both $variable and
>>>>>>>> $reference point to the same memory location. changing one but using
>>>>>>>> the other makes no difference - using either will have the same
>>>>>>>> effect.
>>>>>>>>
>>>>>>>> the second, BY VALUE, means that each variable points to two
>>>>>>>> different locations in memory. the only time they will be equal is
>>>>>>>> when setting them so. once you modify one of them, you have done so
>>>>>>>> idependently of the other - changing one has no effect on the other.
>>>>>>>>
>>>>>>>> hope that makes more sense.
>>>>>>> That was probably the single most unique new concept (pointers and
>>>>>>> address-of) I had conquer when (os so many years ago) I learned C,
>>>>>>> coming from a Fortran background as I did.
>>>>>>>
>>>>>>> Shelly
>>>>>> php references have nothing to do with C-alike pointers.
>>>>>>
>>>>>> Please read the chapter called "references are not pointers" in the
>>>>>> manual.
>>>>>>
>>>>> Yeah, yeah. We still are talking about address-of and not value-of.
>>>>> So there is no explicit pointer variable as there is in C. So what?
>>>>>
>>>>> Shelly
>>>> No, it's not address-of, either in PHP or C++. It's more "alias-of".
>>> ...and by alias of you mean another way of referencing the same place in
>>> memory that contains the value as the thing it is aliasing. --- aka
>>> address-of. Change the value contained in the "reference" and the value
>>> of the "referenced" changes. Change the value located at the "address
>>> of" and the value of the other variable changes. Six of one, a half
>>> dozen of the other. *ptr->foo=junk does the same thing as saying
>>> foo=junk. Also fee=&foo and *fee=junk does the same thing. (It has
>>> been about seven years six I did any C coding (so my memory of exact
>>> syntax may be a little off), but it all comes down to the Bard -- "a
>>> rose by any other name....".
>>>
>> Well, of course everything in the computer has an address. But you should
>> not consider it an address in PHP (PHP doesn't HAVE addresses). It might
>> be referencing a hash value in a table, for instance, and that table may
>> have no fixed address.
>
> well, when dealing with a topic that is hard to explain as it is to a newbie
> who could care less about what php does behind the scenes, a good common
> ground language would be pointers since they are in most other modern
> languages.
>
Well, a newbie has no idea what a "pointer" is. Or what it does behind
the scenes. Many people have never programmed in C/C++, for instance -
and the majority of other languages (Java, Fortran, COBOL, Perl, PASCAL,
Basic... the list goes on) have no concept of pointers.
Pointers are a VERY DIFFICULT subject for people who have never been
exposed to them, no matter what their experience. In my C and C++
classes, it is the most difficult concept for programmers experienced in
non-pointer languages to grasp. In fact, most beginning programmers
have an easier time than experienced ones.
Much better to use non-technical terms, such as "alias".
> i don't think the op is familiar with it anyway based on the way the
> question was posed. that's why my first response demonstrated the behavior
> rather than a technically correct response - one that would have been lost
> any way, on the op.
>
And unnecessarily complicated the description.
>> Additionally, in C++, it is NOT an address. You cannot change what item
>> is being referenced in C++, for instance. It is truly an alias.
>
> actually, if you want to get technical, each variable points to an address
> in memory that address may contain either data for the datatype specified,
> or it may contain a pointer to another address...that may contain either
> data for the datatype specified, or it may contain a pointer to another...
>
Sure. But there is a distinct difference between a pointer and a
reference. COBOL and FORTRAN both have variables. They both have
something which acts like references. But they don't have pointers.
PHP has references. It does not have pointers. What goes on under the
covers is immaterial.
> but, who gives a shit really. we're trying to get a point across that is not
> simply made either way. is this helping the op, or edifying someone else?
>
The person who doesn't understand because you unnecessarily complicated
the explanation with technical gobbly-gook?
>> The difference being in C++ you do have addresses - they are used in
>> pointer variables. And you can change the address (contents of the
>> pointer) to point at another location in memory.
>
> and this is C++? btw, did you not see me change the variables in my example
> from being references to independent 'memory locations'. don't get technical
> here, we're talking about behavior. i did exactly what you said php doesn't
> have the ability to do...if i understand you correctly here.
>
I was discussing C++ implementation with Shelly, not your code.
>> *ptr->foo = junk is NOT the same as foo=junk. *ptr->foo is pointing to a
>> class or structure member (class/structure type unknown) named "foo".
>> foo=junk is referencing a non-class/structure variable. You could say
>> *ptr=junk, but only if ptr contains the address of foo.
>
> arguing his example gets you no where since his point is that you can get
> the same *behavior* from php in most cases that you can in C++ regarding
> references. if you want to go off on semantics, fine. however, remember that
> php is a different animal than C++. that means, in most cases, you're going
> to be comparing apples to oranges.
>
Yes, I know they are different. I am using C++ as an example because it
has both pointers and references. It provides a valid comparison
between the two. You can't make that comparison in PHP because it
doesn't have pointers.
>> Additionally, in C++ you must have an exact match between types on each
>> side - no conversions (i.e. int->double) allowed. References allow
>> conversions (casting is not a conversion!).
>
> this would be an apple and an orange example, case in point! do you expect
> *any scripting* language to *require* strong datatyping? that's one of the
> strengths of scripting languages.
>
Not at all. It's a difference between pointers and references.
> further, are you fully prepared to discuss in a meaningful way to the op,
> how memory works, what conversions are and what casting is...not just how
> php does any of them, but C++ also?
>
I sure can. Can you?
>> I could continue - but there are significant differences between pointers
>> in references in C++.
>
> that's great, however, we're talking about php. essentially, the behavior is
> such, in this example, that making any distinction is just semantics and
> very useless to the op.
>
We are talking about the differences between pointers and references,
using a language which has both. PHP doesn't have pointers.
>>> You say pot-tay-to and I say po-tah-to.
>>>
>>> Shelly
>> Not at all. It is quite important to keep those straight, as I tell my
>> C++ students.
>
> good for them that they have you, i suppose. i'm sure, being the seasoned
> teacher that you are, you wouldn't dare cover such a topic on day one, would
> you?
>
> ;^)
>
>
No, we don't normally get into it until the afternoon of day 2.
But then we do an entire C++ course in 5 days. It's what corporations
want. And I've been doing it for almost 17 years now.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================
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