On 01/02/2015 01:01, Andrea Faulds wrote:
Given that PHP is dynamic, not compiled, and function calls can have side
effects, though, this would be difficult to enforce. You’d need to check that
all calls made within the function do not have any side effects on that value…
I’m not sure how workable this is.
If you can implement copy-on-write, you can implement immutability, and
vice versa. However, any context where its possible to mix mutable and
immutable (or mutable-reference and copy-on-write) would get confusing
very quickly, I think.
Consider some possible behaviours of this set of objects:
$a->b = $b;
$a2 = $a;
$a2->b->value = 42;
If every object is immutable or copy-on-write, this is easy to reason
about: $b and $a->b remain the same, while $a2->b is created as a new
clone; in doing so, $a is separated from $a2 to reference this new copy.
But what if $a/$a2 are immutable, or copy-on-write, but $b is not - do
$b, $a->b and $a2->b all reflect the change, with no error? That would
certainly make no sense for const parameters, and would be a massive
gotcha for "value objects" defined as such at the class (rather than
instance) level.
Regards,
--
Rowan Collins
[IMSoP]
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