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Re: out of sheer curiosity... [message #177564 is a reply to message #177558] Tue, 10 April 2012 00:17 Go to previous messageGo to previous message
Jerry Stuckle is currently offline  Jerry Stuckle
Messages: 2598
Registered: September 2010
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On 4/9/2012 4:50 PM, Thomas Mlynarczyk wrote:
> Jerry Stuckle schrieb:
>
>> In object oriented programming, a new object can ONLY be created by
>> calling a constructor. As noted above, different languages have
>> different terms for them. But a constructor MUST be called according
>> to OO principles.
>
> Just to avoid confusion: When a new object is created, PHP must do some
> work under the hood like allocating memory etc. and this of course is
> "construction" work which is always done and in that sense a constructor
> is indeed always called.
>

No, memory allocation is NOT the same as a constructor. Memory
allocation makes space for the object. The constructor initializes it.

> But after that, there is (or is not) the call to __construct(). And now
> that I think of it, the name __construct() is actually not quite
> correct, since the actual construction of the object is already done at
> that point. What __construct() really does is perform some
> initialization (in Python, the corresponding method is indeed called
> __init__()).
>

In OO terminology, the correct term is "constructor". I'm not familiar
with Python, so I can't say what Python calls it. But the name is not
as important as the job.

> And this initialization is not needed (or might even prove harmful) when
> the object is copied rather than created from scratch, because in that
> case the initialization was already done on the original object and the
> copy was thus created from an already initialized object and it will
> "inherit" the initialized state. Instead, there are __clone() and
> __wakeup() which replace __construct() and can do different
> initialization tasks depending on how the object was created.
>

Initialization is NEVER harmful if it is done properly. That's the
whole purpose of initialization!. wakeup() is NOT a constructor - any
more than sleep() is a destructor.

> Therefore I must correct my earlier remark about neither __clone() nor
> __wakeup() being constructors: __construct(), __clone() and __wakeup()
> are all "of the same kind" -- performing initialization of an object
> depending on how it was created.
>

wakeup() is not a constructor. If you consider it a constructor, then
you must also consider sleep() to be a destructor - in which case it
would be illegal to call the destructor after calling sleep().

> On the other hand, __sleep() is not a destructor, because nothing is
> destroyed when it is called. Note that __sleep() is supposed to return
> an array, contrary to __destruct(). So, while the names __sleep() and
> __wakeup() suggest a correspondence like __destruct() and __construct(),
> this is not the case, since __sleep() is called on the original object,
> while __wakeup() is called on the resurrected copy, so they're not
> called on the same object.
>

It is the opposite of wakeup() - just like __construct() is the opposite
of __destruct(). You can't have it both ways.

> Anyway, I must thank you for making me think more thoroughly about this.
>
> Greetings,
> Thomas
>


--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex(at)attglobal(dot)net
==================

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