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Subject: Re: [PHP-DEV] [RFC] Immutable variables and objects
From: rowan.collins@gmail.com (Rowan Collins)

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Lester Caine wrote on 02/02/2015 09:19:
> This is probably because I still don't understand objects, as I still
> just consider them as arrays with a few more complex elements. I STILL
> work on the basis that is I pass by reference, I can make modifications
> to the data while if I don't I get a copy and have to pass the copy back
> if I need the original changed. This used to be all very simple, so when
> did it stop working? This may explain why I get into trouble with stuff
> that has been working for years but after 'modernising' starts throwing
> problems :(

Since PHP 5, and in most other languages, objects are passed with an 
extra level of indirection, almost but not quite the same as 
pass-by-reference. So there are actually three ways a variable can be 
passed (or assigned):

- scalar by value - an assignment to the variable changes only that variable
- scalar by reference, using & - both variable names point to the same 
variable, and assigning a value to one assigns it to both
- object by value - an assignment to the variable still only changes 
that variable, BUT two variables can point at the same object can both 
modify its internal state. So if you have $current_user = 
getCurrentUserObject(); then saying $current_user = null; is changing 
its value, so would only change that variable, but 
$current_user->setPassword('1234'); is not, so the change would be 
visible from all variables pointing at that object.

Immutable parameters for scalars and arrays are simple: currently you 
can use a by-value parameter as a local variable in your function, but 
you might want to avoid the confusion of this: function foo( const $bar 
) { $bar = 42; // ERROR } or foo( const array $bar ) { $bar[] = 42; // 
ERROR }

Immutable parameters for objects are complicated, because foo( const 
$bar ) { $bar->value = 42; } is not technically changing the *value* of 
that object, but it would be useful to have an enforcement that it 
wouldn't happen.

Hope that clarifies things a bit.
Regards,
-- 
Rowan Collins
[IMSoP]
||

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