Re: [PHP] Re: Enforce a constant in a class.
2010/1/25 Colin Guthrie :
> 'Twas brillig, and Richard Quadling at 22/01/10 11:33 did gyre and gimble:
>> Hello,
>>
>> One of the aspects of an interface is to enforce a public view of a
>> class (as I see it).
>>
>> Within PHP, interfaces are allowed to have constants, but you cannot
>> override them in a class implementing that interface.
>>
>> This seems wrong.
>>
>> The interface shouldn't define the value, just like it doesn't define
>> the content of the method, it only defines its existence and requires
>> that a class implementing the interface accurately matches the
>> interface.
>>
>> Is there a reason for this behaviour?
>>
>>
>>
>> _OR_
>>
>> How do I enforce the presence of a constant in a class?
>>
>> > interface SetKillSwitch {
>> const KILL_SWITCH_SET = True;
>>
>> // Produces an error as no definition exists.
>> // const KILL_SWITCH_NOTES;
>>
>> // Cannot override in any class implementing this interface.
>> const KILL_SWITCH_DATE = '2010-01-22T11:23:32+';
>> }
>>
>> class KilledClass implements SetKillSwitch {
>> // Cannot override as defined in interface SetKillSwitch.
>> // const KILL_SWITCH_DATE = '2010-01-22T11:23:32+';
>> }
>> ?>
>>
>> I want to enforce that any class implementing SetKillSwitch also has a
>> const KILL_SWITCH_DATE and a const KILL_SWITCH_NOTES.
>>
>> I have to use reflection to see if the constant exists and throw an
>> exception when it doesn't.
>>
>> The interface should only say that x, y and z must exist, not the
>> values of x, y and z.
>
> Forgive the perhaps silly question but why are you requiring to use
> constants here.
>
> I appreciate the desire to use Reflection but why not just define a
> method that must be implemented in the interface?
>
> interface SetKillSwitch {
> public function getKillDate();
> public function getKillNotes();
> }
>
>
> By virtue of something impementing the interface, you know the methods
> will exist.
>
> If you want to make implmentation of classes easier, then define and
> abstract class with an appropriate constructor and implementation:
>
>
> abstract class SetKillSwitchAbstract {
> private $_killDate;
> private $_killNotes;
> protected function __construct($killDate, $killNotes)
> {
> $this->_killDate = $killDate;
> $this->_killNotes = $killNotes;
> }
>
> public function getKillDate()
> {
> return $this->_killDate;
> }
>
> public function getKillNotes()
> {
> return $this->_killNotes;
> }
> }
>
>
> You can either put your "implements SetKillSwitch" in this class or the
> derived classes depending on other methods you want to provide in the
> base class.
>
>
> I don't see why constants specifically are needed here. Rather than
> using reflection you can just use instanceof or similar to tell if a
> given object implements the interface or simply use the interface name
> as a type specifier on an argument to another function/method etc.
>
>
> Col
>
>
> --
>
> Colin Guthrie
> gmane(at)colin.guthr.ie
> http://colin.guthr.ie/
>
> Day Job:
> Tribalogic Limited [http://www.tribalogic.net/]
> Open Source:
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>
>
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>
>
With a constant, PhpDoc will pick up the value of the constant and
incorporate it into the documentation.
With a method, there is no way to know the return value. The type,
sure, but not the value.
Setting a constant is by far the simplest way to deal with this.
A method to return a constant is one method unneeded.
But, as I've said, I completely missed defined().
That's all I needed.
If the kill interface is applied to a class, then the parent class can
quite happily use defined(get_called_class() . '::KILL_SWITCH_SET') to
see if the class is defunct (or whatever).
Really. It was just the defined() call I missed. Everything is now working fine.
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[PHP] Re: Enforce a constant in a class.
'Twas brillig, and Richard Quadling at 22/01/10 11:33 did gyre and gimble:
> Hello,
>
> One of the aspects of an interface is to enforce a public view of a
> class (as I see it).
>
> Within PHP, interfaces are allowed to have constants, but you cannot
> override them in a class implementing that interface.
>
> This seems wrong.
>
> The interface shouldn't define the value, just like it doesn't define
> the content of the method, it only defines its existence and requires
> that a class implementing the interface accurately matches the
> interface.
>
> Is there a reason for this behaviour?
>
>
>
> _OR_
>
> How do I enforce the presence of a constant in a class?
>
> interface SetKillSwitch {
> const KILL_SWITCH_SET = True;
>
> // Produces an error as no definition exists.
> // const KILL_SWITCH_NOTES;
>
> // Cannot override in any class implementing this interface.
> const KILL_SWITCH_DATE = '2010-01-22T11:23:32+';
> }
>
> class KilledClass implements SetKillSwitch {
> // Cannot override as defined in interface SetKillSwitch.
> // const KILL_SWITCH_DATE = '2010-01-22T11:23:32+';
> }
> ?>
>
> I want to enforce that any class implementing SetKillSwitch also has a
> const KILL_SWITCH_DATE and a const KILL_SWITCH_NOTES.
>
> I have to use reflection to see if the constant exists and throw an
> exception when it doesn't.
>
> The interface should only say that x, y and z must exist, not the
> values of x, y and z.
Forgive the perhaps silly question but why are you requiring to use
constants here.
I appreciate the desire to use Reflection but why not just define a
method that must be implemented in the interface?
interface SetKillSwitch {
public function getKillDate();
public function getKillNotes();
}
By virtue of something impementing the interface, you know the methods
will exist.
If you want to make implmentation of classes easier, then define and
abstract class with an appropriate constructor and implementation:
abstract class SetKillSwitchAbstract {
private $_killDate;
private $_killNotes;
protected function __construct($killDate, $killNotes)
{
$this->_killDate = $killDate;
$this->_killNotes = $killNotes;
}
public function getKillDate()
{
return $this->_killDate;
}
public function getKillNotes()
{
return $this->_killNotes;
}
}
You can either put your "implements SetKillSwitch" in this class or the
derived classes depending on other methods you want to provide in the
base class.
I don't see why constants specifically are needed here. Rather than
using reflection you can just use instanceof or similar to tell if a
given object implements the interface or simply use the interface name
as a type specifier on an argument to another function/method etc.
Col
--
Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/
Day Job:
Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
Mandriva Linux Contributor [http://www.mandriva.com/]
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Trac Hacker [http://trac.edgewall.org/]
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Re: [PHP] Re: Enforce a constant in a class.
2010/1/25 Pete Ford :
> Richard Quadling wrote:
>>
>> 2010/1/22 Pete Ford :
>>>
>>> IMHO, a constant is not the correct beastie in this case - if you want it
>>> to
>>> be different depending on the implementation then it ain't a constant!
>>>
>>> You should probably have protected static variables in the interface, and
>>> use the implementation's constructor to set the implementation-specific
>>> value (or override the default)
>>>
>>> interface SetKillSwitch
>>> {
>>> protected static $isSet = TRUE;
>>> protected static $notes;
>>> protected static $date = '2010-01-22T11:23:32+';
>>> }
>>>
>>> class KilledClass implements SetKillSwitch
>>> {
>>> public function __construct()
>>> {
>>> self::$isSet = FALSE;
>>> self::$date = '2010-01-21T09:30:00+';
>>> self::$notes = "Test";
>>> }
>>> }
>>>
>>> Cheers
>>> Pete Ford
>>
>> And of course, "Fatal error: Interfaces may not include member variables".
>>
>>
>>
>
> Ooops, sorry :)
>
> I tend to end up using abstract base classes rather than interfaces for that
> sort of reason...
>
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>
>
Essentially I was starting with the idea that a subclass with constant
X _MUST_ have constant Y and Z. That's what I wanted to enforce.
But, finding that defined() was enough, I now realize that Y and Z are
_not_ mandatory, but they are constants. So simply ...
$KillSwitchNotes = defined(get_called_class() . '::KILL_SWITCH_NOTES') ?: Null;
is enough and now the whole _MUST_ is gone and is now optional.
Much better.
Thank you to everyone who chipped in. Old dog should really have known
that old trick!
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Re: [PHP] Re: Enforce a constant in a class.
Richard Quadling wrote:
2010/1/22 Pete Ford :
IMHO, a constant is not the correct beastie in this case - if you want it to
be different depending on the implementation then it ain't a constant!
You should probably have protected static variables in the interface, and
use the implementation's constructor to set the implementation-specific
value (or override the default)
interface SetKillSwitch
{
protected static $isSet = TRUE;
protected static $notes;
protected static $date = '2010-01-22T11:23:32+';
}
class KilledClass implements SetKillSwitch
{
public function __construct()
{
self::$isSet = FALSE;
self::$date = '2010-01-21T09:30:00+';
self::$notes = "Test";
}
}
Cheers
Pete Ford
And of course, "Fatal error: Interfaces may not include member variables".
Ooops, sorry :)
I tend to end up using abstract base classes rather than interfaces for
that sort of reason...
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Re: [PHP] Re: Enforce a constant in a class.
2010/1/22 Pete Ford :
> IMHO, a constant is not the correct beastie in this case - if you want it to
> be different depending on the implementation then it ain't a constant!
>
> You should probably have protected static variables in the interface, and
> use the implementation's constructor to set the implementation-specific
> value (or override the default)
>
> interface SetKillSwitch
> {
> protected static $isSet = TRUE;
> protected static $notes;
> protected static $date = '2010-01-22T11:23:32+';
> }
>
> class KilledClass implements SetKillSwitch
> {
> public function __construct()
> {
> self::$isSet = FALSE;
> self::$date = '2010-01-21T09:30:00+';
> self::$notes = "Test";
> }
> }
>
> Cheers
> Pete Ford
And of course, "Fatal error: Interfaces may not include member variables".
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Re: [PHP] Re: Enforce a constant in a class.
2010/1/22 Pete Ford :
>
> IMHO, a constant is not the correct beastie in this case - if you want it to
> be different depending on the implementation then it ain't a constant!
>
> You should probably have protected static variables in the interface, and
> use the implementation's constructor to set the implementation-specific
> value (or override the default)
>
> interface SetKillSwitch
> {
> protected static $isSet = TRUE;
> protected static $notes;
> protected static $date = '2010-01-22T11:23:32+';
> }
>
> class KilledClass implements SetKillSwitch
> {
> public function __construct()
> {
> self::$isSet = FALSE;
> self::$date = '2010-01-21T09:30:00+';
> self::$notes = "Test";
> }
> }
>
> Cheers
> Pete Ford
There is the problem. The interface is just saying that a killswitch
has been set. Not the date it was set, nor the notes. Thats specific
to the implentor.
In the implementor, they are constant.
In my mind, the interface is only saying that these elements need to
exist. Not what they are. Just like if I say there must be a method
X() in the interface, I don't define what it does.
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[PHP] Re: Enforce a constant in a class.
Richard Quadling wrote:
Hello,
One of the aspects of an interface is to enforce a public view of a
class (as I see it).
Within PHP, interfaces are allowed to have constants, but you cannot
override them in a class implementing that interface.
This seems wrong.
The interface shouldn't define the value, just like it doesn't define
the content of the method, it only defines its existence and requires
that a class implementing the interface accurately matches the
interface.
Is there a reason for this behaviour?
_OR_
How do I enforce the presence of a constant in a class?
I want to enforce that any class implementing SetKillSwitch also has a
const KILL_SWITCH_DATE and a const KILL_SWITCH_NOTES.
I have to use reflection to see if the constant exists and throw an
exception when it doesn't.
The interface should only say that x, y and z must exist, not the
values of x, y and z.
Regards,
Richard.
--
-
Richard Quadling
"Standing on the shoulders of some very clever giants!"
EE : http://www.experts-exchange.com/M_248814.html
EE4Free : http://www.experts-exchange.com/becomeAnExpert.jsp
Zend Certified Engineer : http://zend.com/zce.php?c=ZEND002498&r=213474731
ZOPA : http://uk.zopa.com/member/RQuadling
IMHO, a constant is not the correct beastie in this case - if you want
it to be different depending on the implementation then it ain't a constant!
You should probably have protected static variables in the interface,
and use the implementation's constructor to set the
implementation-specific value (or override the default)
interface SetKillSwitch
{
protected static $isSet = TRUE;
protected static $notes;
protected static $date = '2010-01-22T11:23:32+';
}
class KilledClass implements SetKillSwitch
{
public function __construct()
{
self::$isSet = FALSE;
self::$date = '2010-01-21T09:30:00+';
self::$notes = "Test";
}
}
Cheers
Pete Ford
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