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In-Reply-To: <9BB32AF2-E776-46CA-8604-0B5283B5050C@strojny.net>
Date: Tue, 21 Oct 2014 00:39:25 +0100
Cc: PHP Internals <internals@lists.php.net>
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Message-ID: <AAB776CE-D764-4834-8B3B-F0373105F637@ajf.me>
References: <66B7B28C-2651-4A71-AC2A-55D4C7BB3DDC@ajf.me> <9BB32AF2-E776-46CA-8604-0B5283B5050C@strojny.net>
To: Lars Strojny <lars@strojny.net>
Subject: Re: [PHP-DEV] [RFC] Safe Casting Functions
From: ajf@ajf.me (Andrea Faulds)


> On 21 Oct 2014, at 00:27, Lars Strojny <lars@strojny.net> wrote:
>=20
> I like the proposal except for one thing: the functions returning =
false in case of an error. As the next logical function would be =
"to_bool()", I foresee a lot of trouble with regards to API design as =
returning false there either means successful cast to false or an error =
while casting. What about changing the functions to take an $isError =
variable as a second argument?
>=20
> $value =3D to_string(1.2, $isError);
> if ($isError) {
>   ...
> }
>=20
> Alternatively one could do the same thing with an $isSuccess variable:
>=20
> $value =3D to_string(1.2, $isSuccess);
> if (!$isSuccess) {
>   ...
> }
>=20
> Thoughts?

This is an interesting question. It=E2=80=99s actually one I=E2=80=99d =
considered myself, I think I briefly mention it in the RFC. However, I =
don=E2=80=99t expect it to be a problem, and the reason is really quite =
simple: There=E2=80=99s no clear-cut one-size-fits all boolean casting =
function you could make, and booleans are trivial to validate yourself.

Adding something like is_bool() would be possible, the problem is what =
behaviour it would have, and there are too many possibilities. Do you =
accept 1 and 0? If so, do you accept all non-zero values, or not? Is =
=E2=80=9Ctrue=E2=80=9D TRUE or is it FALSE? Is =E2=80=9Cyes=E2=80=9D =
TRUE or is it FALSE? Do =E2=80=9Ctrue=E2=80=9D and =E2=80=9Cyes=E2=80=9D =
validate? Do they not? Does the empty string validate? Does it not? Bear =
in mind that boolean casting was one of the most problematic areas of =
the abandoned Scalar Type Hinting RFC: there=E2=80=99s no clear set of =
definitely boolean values, nor a clear idea of which mean which boolean =
value. Basically, I don=E2=80=99t think we=E2=80=99d ever be able to =
draw the line.

The other thing is, well, there=E2=80=99s not really a need. You can =
quite simply do something like this: if ($value !=3D=3D =E2=80=9Ctrue=E2=80=
=9D && $value =3D=3D=3D =E2=80=9Cfalse=E2=80=9D) { /* error! */ } - and =
while this is less convenient than is_bool, as I mentioned before, =
there=E2=80=99s no real agreement on what is_bool should do so you=E2=80=99=
d have to do this anyway. A thought: A weird, but workable solution for =
one particular style is [=E2=80=9Ctrue=E2=80=9D =3D> TRUE, =E2=80=9Cfalse=E2=
=80=9D =3D> FALSE][$value] ?? NULL - whether that=E2=80=99s a wonderful =
or horrible use of PHP is up to you. ;)

So I don=E2=80=99t think using FALSE here is a problem, since I doubt =
is_bool would ever be added.

Regarding using a reference variable for the output, I don=E2=80=99t =
like that idea much. It doesn=E2=80=99t chain very well=E2=80=A6 and =
would it fail a strict type hint, if we added that? Even if it somehow =
did, I don=E2=80=99t think it is a good idea. Since I don=E2=80=99t =
think is_bool will happen, there=E2=80=99s also no real need, either.
--
Andrea Faulds
http://ajf.me/