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Subject: Re: [PHP-DEV] [RFC] Immutable variables and objects
From: cryptocompress@googlemail.com (Crypto Compress)


>> The with*() methods in PSR-7 are documented to return a new instance,
>> not modify the existing instance.  Yes, there's no way in PHP itself to
>> force that syntactically, which is why documentation exists. :-)
>>
>> Also, in the benchmarks we've run the performance cost of all those new
>> objects is measured in nanoseconds, ie, small enough that we're not
>> worried about it.  (Hats off to the PHP Internals folks for making that
>> fast!)
> It is great that this is fast, but I wonder (maybe off-topic?) why do
> it? I.e. it is clear that in something like:
>
> $a = new Request->withHeaders(...)->withBody(...)
> ->withEncoding(...)->withETag(...)
>
> the intermediate objects are useless and nobody needs 5 new objects when
> you do it. Am I missing something here?

Hi,

my assumptions after some testing:
- This is only true in case of reassigning ($a = clone $a) the old 
variable, as refcount for underlying values remains 1 for all values in 
clones, so cow don't need to copy anything.
- If the old object is not thrown away, then memory consumption is 
doubled and the "fast" argument is wrong.
(Performance, of cloning an object without copying values and of some 
method calls, is negligible.)

Omit mutator methods (with*/set*) is a simple and logical way to achieve 
immutability in PHP. No need for const/final/...