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Message by Jerry Stuckle is ignored  [reveal message]  [reveal all messages by Jerry Stuckle]  [stop ignoring this user] Go to previous messageGo to next message
Re: Object constructors/destructors [message #185152 is a reply to message #185149] Sun, 02 March 2014 17:14 Go to previous messageGo to next message
Richard Damon is currently offline  Richard Damon
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On 3/2/14, 3:42 PM, Jerry Stuckle wrote:
> On 3/2/2014 2:28 PM, Richard Damon wrote:
>> On 3/1/14, 2:22 PM, Jerry Stuckle wrote:
>>> On 3/1/2014 12:56 PM, Richard Damon wrote:
>>>> On 2/27/14, 8:25 AM, Jerry Stuckle wrote:
>>>> > On 2/26/2014 11:49 PM, Richard Damon wrote:
>>>> >> On 2/26/14, 8:44 AM, Jerry Stuckle wrote:
>>>> >>> On 2/26/2014 7:50 AM, Richard Damon wrote:
>>>> >>>>
>>>> >>>> An the "name" of the Deserializing constructor in PHP is
>>>> >>>> __wakeup().
>>>> >>>>
>>>> >>>> You also do NOT get two destructor calls on the same object, the
>>>> >>>> deserializing created a new object.
>>>> >>>>
>>>> >>>
>>>> >>> __wakeup() is not a constructor - and does not do the same thing.
>>>> >>>
>>>> >>
>>>> >> What makes it NOT a constructor? IT seems to be exactly the thing
>>>> >> that
>>>> >> does what you say must be done to make the new object via
>>>> >> unserialization.
>>>> >>
>>>> >
>>>> > If you want to consider __wakeup() to be a constructor, then you must
>>>> > consider __sleep() to be a destructor. In that case, PHP is also
>>>> > wrong
>>>> > because if an object is serialized, it will call both __sleep() and
>>>> > the
>>>> > destructor. This would be two calls to destructors for the same
>>>> > object.
>>>> >
>>>>
>>>> WHY does __sleep() need to be a destructor?
>>>>
>>>> __sleep() is a function to control how an object is serialized, and the
>>>> object, as you seem to know, still exists, so no destructor should
>>>> happen at this point, in fact, if you look at it, __sleep() has not
>>>> expected to have any effect on the current object, its purpose is to
>>>> make sure that __wakeup() will get all the data it needs, and allow the
>>>> removal of data that it won't need.
>>>>
>>>
>>> If you are going to claim __wakeup() is a constructor, then you have to
>>> agree that it's opposite (__sleep()) is a destructor. Otherwise you are
>>> being inconsistent.
>>>
>>> You can't just make up rules as you see fit!
>>>
>>
>> Then why are you claiming that something that isn't a desturctor must be
>> one.
>>
>
> I'm not - you're the one claiming __wakeup() is a constructor, but it's
> opposite, __sleep() is not a destructor.
>
>> Serialization, creates an external representation for an object, that is
>> what __sleep() is part of. This does NOT inherently involve the
>> destruction of the object (at least at that point).
>>
>
> Then __wakeup() does NOT inherently involve creation of an object.
>

Since __wakeup() is (naturally) invoked as part of the deserializing
operation, and since PHP defines deserialization via a factory function
that returns the deserialized object, and thus creates an object, is, BY
DEFINITION, a construction operation. __wakeup() is part of that
process, to allow the programmer to do any parts of the construction
process that isn't automatically done.

I suppose if you want to be very pedantic, unserialize() is actually the
unserializing constructor for every object, of which __wakeup() is the
programmer definable class specific piece of it.

>> Deserialization, on the other hand, creates an object from an external
>> representation. so it will involve the construction of a new object (you
>> can do "in-place" deserialization in some languages, where you first
>> create a dummy object, and then fill it in with the external data, but
>> this is normally a clumsy way to define it).
>>
>
> Not in other languages. It builds from an already existing object where
> the constructor has been called.

Some cases use something like:

Type obj;
obj.unserialize(source);

This default constructs the object first, then serializes into the
object. For this to work, the object must not have any "constant"
members that need to be unserialized. For this method, unserialization
is not construction.

Other cases you use

Type obj(source);

or

Type *obj = new Type(source);

or even

Type *obj = unserializing_factory(source)

In these cases, the object is directly created from the serialization
source, and thus DOES involve a constructor and you do not run into the
problem of constant members. In the last case, the calling program
doesn't even need to know the exact type of the object, just a base
type, and the factory can determine the exact type from the data source.
unserializing_factory might be a global function, or it might be a
static member of the base type Type.

This last case is in fact, the method used in PHP. Since PHP is a
totally dynamically typed language, there is a single global function
that does this operation, and the serialization format defines what type
of object is to be created. It uses the "magic method" __wakeup() to
provide it with the type specific parts of the operation.

>
>> Note that the object oriented paradigm does have asymmetry in it. A
>> given type will tend to have multiple constructors, for the different
>> ways that an object might come into existence. There is usually only one
>> destructor. In PHP, one of these constructors is called __construct()
>> which is the general purpose constructor. (unlike in other statically
>> type languages, we can only define one of these). PHP also lets us
>> define a piece of the deserialing constructor with __wakeup() (PHP does
>> some of the heavy lifting here in parsing the serialized data and
>> setting up the object, __wakeup() is just required to do any final
>> needed operations after the values have been set.)
>>
>
> Constructors are constructors, and the destructor is a destructor. No
> asymmetry there. Except in PHP.
>
>

The asymmetry is that a type will, often, have many different
constructors defined: Default, copy, conversion, etc each taking some
data source, an making an object out of that. One such constructor might
be a deserializing constructor that creates a new object out of a data
source that was specially built by serializing a different object.

A type will almost exclusively have a single destructor. This difference
in number is the asymmetry I was referring to.

PHP does not differ here, all objects are created with some form of
"constructor", although PHP does not call all of them constructors.

__construct() is used when creating an object via new
__clone() is used when creating an object via clone
__wakeup() is used when creating an object via unserialize()

All of the magic functions have the role of a constructor.

Your confusion here is probably due to the less than rigorous method
used to document this in PHP, it isn't clear that the PHP term
"constructor" is different than the same term you learned in your object
oriented class.
Message by Jerry Stuckle is ignored  [reveal message]  [reveal all messages by Jerry Stuckle]  [stop ignoring this user] Go to previous messageGo to next message
Re: Object constructors/destructors [message #185154 is a reply to message #185153] Sun, 02 March 2014 18:05 Go to previous message
Tim Streater is currently offline  Tim Streater
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In article <lf0cgi$c21$1(at)dont-email(dot)me>, Jerry Stuckle
<jstucklex(at)attglobal(dot)net> wrote:

> On 3/2/2014 5:14 PM, Richard Damon wrote:
>> On 3/2/14, 3:42 PM, Jerry Stuckle wrote:
>>> On 3/2/2014 2:28 PM, Richard Damon wrote:
>>>> On 3/1/14, 2:22 PM, Jerry Stuckle wrote:
>>>> > On 3/1/2014 12:56 PM, Richard Damon wrote:
>>>> >> On 2/27/14, 8:25 AM, Jerry Stuckle wrote:
>>>> >>> On 2/26/2014 11:49 PM, Richard Damon wrote:
>>>> >>>> On 2/26/14, 8:44 AM, Jerry Stuckle wrote:
>>>> >>>>> On 2/26/2014 7:50 AM, Richard Damon wrote:

[shitloads snipped]

>> Your confusion here is probably due to the less than rigorous method
>> used to document this in PHP, it isn't clear that the PHP term
>> "constructor" is different than the same term you learned in your object
>> oriented class.

> You are like some others here - you'll argue just to argue. There is
> nothing new here - and you're still wrong.
>
> But I'm not going to try to teach the pig to sing any longer.

How about the pair of you learn how to snip, eh? Or is that too
difficult?

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