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Re: Operator precedence [message #185034 is a reply to message #185032] Tue, 25 February 2014 00:07 Go to previous messageGo to previous message
Christoph Michael Bec is currently offline  Christoph Michael Bec
Messages: 207
Registered: June 2013
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Thomas 'PointedEars' Lahn wrote:

> Ben Bacarisse wrote:
>
>> Thomas 'PointedEars' Lahn <PointedEars(at)web(dot)de> writes:
>>> Ben Bacarisse wrote:
>>>> […] Expressions are built from operators, but is ',' an operator in PHP?
>>>> It appears in the operator precedence table but it isn't an operator in
>>>> an sense that would normally be understood by someone familiar with
>>>> these terms.
>>>
>>> ECMAScript has a “Comma Operator”, too.
>>
>> But my point was the PHP doesn't have one --
>
> But it does:
>
> for ($i = 0, $j = 42; $i < $j; ++$i);
> ^

The comma is used in sevaral places in the PHP grammar[1]. However,
IMHO your example (inside a for_expr) is the only case where the comma
is used as an operator. The other uses are for declaration and
parameter lists (spoken in a broad sense).

>> not in any normal sense of the word.
>
> Please define what you consider to be an operator in a “normal sense of the
> word”.

It might be defined as an operator that can be used in arbitrary
expressions. Consider the following ECMAScript expression:

a = 1, b = 2;

The "equivalent" expression in PHP is a syntax error:

$a = 1, $b = 2;

>> ECMAScript really does have one (like C and C++ do).
>
> Why do you think C and C++ have a comma operator (like ECMAScript)?

According to the C grammar[2]:

exp : assignment_exp
| exp ',' assignment_exp

[1] <http://lxr.php.net/xref/PHP_5_5/Zend/zend_language_parser.y>
[2] <http://www.cs.man.ac.uk/~pjj/bnf/c_syntax.bnf>

--
Christoph M. Becker
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