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Date: Tue, 17 Nov 2015 11:04:04 +0000
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Subject: Re: [PHP-DEV] Immutable modifier
From: rowan.collins@gmail.com (Rowan Collins)

Hi Andrea,

Andrea Faulds wrote on 17/11/2015 01:47:
> Larry Garfield wrote:
>> The "everything in the constructor" is the problem.  That results in,
>> essentially, an obscenely long function call that just happens to be
>> named __construct().  If I wanted something that obscure and hard to
>> work with I'd just use anonymous arrays. :-)
>
> Huh?
>
> "with" methods and __construct are not exclusive. In fact, you could 
> have a private constructor and only have "with" methods. Only allowing 
> assignment to properties in the constructor doesn't prevent having a 
> nice API: have your methods call the constructor.
>
> I don't see what you're getting at here.
>

Making the "with" methods wrap the constructor tidies the public API, 
but that (private) constructor needs to be just as complex as Larry said 
earlier - you've got to manually extract all the properties of one 
instance, and pass them as parameters to the other. Or, you could copy 
them one by one inside the body of the constructor, which comes to the 
same thing - lots of boilerplate.

If you look at the PSR-7 implementation I linked to earlier [1], there's 
no such boilerplate, just a single call to "clone $this", and PHP does 
it all for you. But that doesn't work with a simplistic definition of 
immutable like "mutable in constructor" or "mutable until non-null"; you 
need to be able to "freeze" an instance once you've set it up, or have 
privileged (private) methods which are allowed to mutate the properties.

[1] https://github.com/guzzle/psr7/blob/master/src/Request.php#L101

Regards,
-- 
Rowan Collins
[IMSoP]