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Date: Fri, 10 Mar 2017 12:57:42 +0200
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To: "internals@lists.php.net" <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] [Discussion] is_string(), string type and objects
 implementing __toString()
From: narf@devilix.net (Andrey Andreev)

Hi,

On Thu, Mar 9, 2017 at 7:47 PM, Fleshgrinder <php@fleshgrinder.com> wrote:
> On 3/9/2017 12:47 PM, Andrey Andreev wrote:
>> How can "any other scalar value" work? Using the cookie and headers examples:
>>
>> - booleans can be used as On/Off flags for the secure and httpOnly
>> cookie attributes, but aren't valid literal values for any of the
>> attributes, or any HTTP header.
>> - integers are valid as a few headers' values - that is true, but
>> certainly in a minority of cases
>> - floats may be used for the q(uality) attribute in content
>> negotiation (and nothing else AFAIK), but that is a very, very narrow
>> domain
>> - null is obviously invalid ... who sends an empty header? And if you
>> have a use case where you do want to use them, we can already make
>> anything nullable
>>
>> Of course the string values should be validated, unless you want to
>> allow setting arbitrary headers, e.g.:
>>
>>     abstract function setHeader(stringable $name, stringable $value);
>>
>> ... but filtering out the known to be invalid types *is* validation.
>> And just that much better if it happens at compile time.
>
> Because:
>
> - bool(true)  = '0'
> - bool(false) = '1'
> - int(n)      = 'n'
> - float(n)    = 'n'
> - null        = ''
> - object(s)   = 's'
> - string(s)   = 's'
>
> All values are possible values that I can pass to you if you use the
> string type constraint. Hence, all these types are valid string values
> if you request a stringable.
>

Yes, they're valid string values, but the examples I gave were meant
to show that context can make them predictably invalid, and hence why
strict typing is desirable.

> Stringable should work exactly like the string constraint in non-strict
> mode, but regardless of the strict mode. The difference to a scalar type
> constraint is that the passed values are always converted to a scalar
> string, hence, the source type is unknown to the receiver.
>

I'm not really interested in making "strict mode" less strict - it's
already opt-in and non-enforceable.
I want ways to write stonger-type code in "non-strict mode", because
the fact that "strict mode" is non-enforceable means I can never rely
on it.

Cheers,
Andrey.