covariant return & contravariance

potatoCode

Hello php experts!

I'm trying to get my head around php OOP and need some clarification.
My understanding is that php variables can hold any data type without
explicitly declaring its type.

Judging from this fact, am I correct in saying that

A. php supports covariant return, but does not enforce contravariance.
B. slicing still occurs in inheritance.

Thanks.

NogDog

potatoCode;10923744 wrote:
Hello php experts!

I'm trying to get my head around php OOP and need some clarification.
My understanding is that php variables can hold any data type without
explicitly declaring its type.

Yes, the type of any variable's value is decided at run-time, either due to explicit setting via casting or [man]settype/man, or else by implicitly determined type based on context. The type can be changed at any time when a new value is assigned, and automatic "type juggling" can occur whenever a variable of one type is used in the context of another type.

Judging from this fact, am I correct in saying that

A. php supports covariant return, but does not enforce contravariance.
B. slicing still occurs in inheritance.

I'm afraid I'm not smart enough to know what you are asking, let alone the answer. 😕 I'm sure Weedpacket, Laserlight or one of the other better educated programmers here will be along soon to provide some feedback.

laserlight

potatoCode wrote:
A. php supports covariant return, but does not enforce contravariance.

The return type is not specified when declaring a function, so the notion of covariant return types is something of a moot point: you could override a method to return a completely different type, and define functions that return completely different types depending on the flow of control. As for enforcing contravariance in parameters: type hinting allows this, to some extent.

potatoCode wrote:
B. slicing still occurs in inheritance.

PHP 5 objects are pointers without pointer syntax (and on which pointer arithmetic cannot be performed). As such, type slicing does not occur.

potatoCode

Hi my forever idol!

laserlight;10923752 wrote:
The return type is not specified when declaring a function, so the notion of covariant return types is something of a moot point:

Funny that's what I thought to myself right after I clicked submit button.
Since php has garbage collection, and the built-in arrays themselves are dynamic,
is it pretty much useless to write a container-like class?
(other than to wrap and simplify)

PHP 5 objects are pointers without pointer syntax (and on which pointer arithmetic cannot be performed). As such, type slicing does not occur.

Hm, I must say that's going to take some getting used to :glare:

Is there a case where one needs to worry about memory leak despite having a GC?
(just asking...)

thanks.

potatoCode

NogDog;10923751 wrote:
Yes, the type of any variable's value is decided at run-time, either due to explicit setting via casting or [man]settype/man, or else by implicitly determined type based on context. The type can be changed at any time when a new value is assigned, and automatic "type juggling" can occur whenever a variable of one type is used in the context of another type.

Hello NogDog,
Thanks for the introduction to some new functions.
I'm earning much from you. 🙂

I'm afraid I'm not smart enough to know what you are asking, let alone the answer. 😕 I'm sure Weedpacket, Laserlight or one of the other better educated programmers here will be along soon to provide some feedback.

I'm afraid it's me who's in the fault.
I'm trying to unlearn something first.
So chances are that I'd be asking stupid questions that don't have any bearings
toward learning the php langauge the right way.
(but of course, I don't know how relevant the questions would be in the first place xD)
So please excuse me whenever I do so.

Thanks!

NogDog

potatoCode;10923758 wrote:
...
Is there a case where one needs to worry about memory leak despite having a GC?
(just asking...)

If there is, it probably would be considered a bug in PHP, not a programmer error. (Maybe if you're using something like the [man]memcached[/man] functions you could eat up memory, though it probably would not strictly be considered a memory leak in the usual sense.)

potatoCode

Okay,
I'll look into that.
Thanks NogDog.