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Date: Wed, 24 Jan 2018 19:39:14 -0600
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Subject: [PHP-DEV][RFC][DISCUSSION] Collection Inspection
From: tendoaki@gmail.com (Michael Morris)

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Ok, here's another idea I've been mulling over. This I know is possible
because I've done it using user land code, specifically Drupal 8's
Assertion\Inspector class.

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Component%21Assertion%21Inspector.php/class/Inspector/8.5.x

These methods provide a means to inspect collections - arrays usually but
also Traversables. They fill a hole in the PHP library - the ability to
check collection integrity.

To answer the question "Why in core?" - well, Drupal needing to do this
using a library referenced only by assert() statements creates an
undocumented dependency for any class that wants to run these checks. From
a pragmatic standpoint it just feels wrong.  Most other languages have some
means of doing these checks.




IMPLEMENTATION STYLE #1:  collectionof operator
The style of implementation I like the most is a collectionof operator in
parallel to the instance_of operator.  It would be instanceof's plural
brother, so

$arg collectionof \SomeClass

To pass the check $arg must be of the iterable psuedotype with all its
values being a \SomeClass object.

This is all well and good, but collection integrity checks are usually
going to be looking to see if all the members are the same scalar.

$arg collectionof string

For language consistency we would need to allow instance_of to do the same,
which it currently does not.

$arg instanceof string

This does create duplication with the is_* family of functions, but
instanceof already overlaps is_a heavily.



IMPLEMENTATION STYLE #2: all_*
This style takes the is_* family and creates plural cousins for them.
Example:

all_string($arg);

This is most similar to the user land solution. Following the current is_*
family this gives us all_array(), all_bool(), all_callable(), all_double(),
all_float(), all_int(), all_integer(), all_iterable(), all_long(),
all_null(), all_numeric(), all_object(), all_real(), all_scalar(), and
all_string(). One other function, all_are(), would be necessary for class
and interface inspection.

That's a lot of new functions, and the chance of BC breaking with someone's
code is very high, so I don't personally like this approach. I'm putting it
out there as alternate because despite that shortcoming it is a sensible
alternative.

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