Doc #76875 [Com]: It is not clear what 'uncomparable' means
Edit report at https://bugs.php.net/bug.php?id=76875&edit=1
ID: 76875
Comment by: viveksrivastab58 at gmail dot com
Reported by: manabu dot matsui at gmail dot com
Summary: It is not clear what 'uncomparable' means
Status: Open
Type: Documentation Problem
Package: Documentation problem
PHP Version: Irrelevant
Block user comment: N
Private report: N
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[2018-09-14 00:34:32] manabu dot matsui at gmail dot com
I can see that there are uncomparable arrays. However, it is a problem that what kind of results can
be expected (or should not be expected) when doing comparative operations on them is not clear.
For example, if it is guaranteed that $x <= $y and $x> = $y are false for uncomparable arrays
$x, $y, then a function to determine whether two arrays can be compared is able to be written as
follows:
<?php
function isComparable(array $x, array $y)
{
    return $x <= $y || $x >= $y;
}
?>
If it is not guaranteed (eg like 'undefined behavior' in C or 'unspecified
behavior' in Scheme), it must be implemented in a different way.
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[2018-09-13 11:26:31] a at b dot c dot de
"Uncomparable" means "cannot be compared". That means there is no well-ordering
on arbitrary arrays that allows such comparisons to be made in any sensible fashion (how do _you_
think $x and $y should be ordered?).
['a' => 1] < ['b' => 2], for one, evaluates to FALSE because
['a' => 1] is not less than ['b' => 2]. (The operator is defined as
returning TRUE if its left argument is less than its right. This is not the case here.)
In the same way, ['a' => 1] > ['b' => 2] is FALSE because
['a' => 1] is not greater than ['b' => 2] and ['a' => 1] ==
['b' => 2] is FALSE because ['a' => 1] is not equal to ['b'
=> 2].
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[2018-09-13 01:11:19] manabu dot matsui at gmail dot com
Description:
------------
---
From manual page: http://www.php.net/language.operators.comparison
---
In table 'Comparison with Various Types', it is said that 'if key from operand 1 is
not found in operand 2 then arrays are uncomparable', and according to Example 2, the
standard_array_compare function returns null in that case.
When I actually tried it, each operator returned the following value.
<?php
$x = ['a' => 1];
$y = ['b' => 2];
var_dump($x < $y); # false
var_dump($x <= $y); # false
var_dump($x > $y); # false
var_dump($x >= $y); # false
var_dump($x <=> $y); # 1
?>
I can not explain this result from the manual description. I think it would be better to explain
more clearly.
What is the meaning of 'uncomparable'? For example, the following can be considered
* If $x and $y are uncomparable, $x < $y, $x <= $y, $x > $y, $x >=$y are all false, and
$x <=> $y is 1.
* It returns some kind of value, but it is indeterminate what the value is. (The above example
happened to be so, in different situations it could be different results)
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Edit this bug report at https://bugs.php.net/bug.php?id=76875&edit=1
Thread (4 messages)