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Re: Operator precedence [message #185049 is a reply to message #185032] Tue, 25 February 2014 03:08 Go to previous messageGo to previous message
Ben Bacarisse is currently offline  Ben Bacarisse
Messages: 82
Registered: November 2013
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Thomas 'PointedEars' Lahn <PointedEars(at)web(dot)de> writes:

> 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);

But try this:

for (($i = 0, $j = 42); $i < $j; ++$i);

In general, putting an expression in parentheses does not stop it being
an expression. The permission to use ',' in a for statement is special
syntax: it's not part of the syntax for an expression. To give another
example, if the ',' in a for statement built an expression you should be
able to change:

for ($i = 0; f($1), $i < 10; $i++) { ...; }

into

$i = 0;
while (f($1), $i < 10) { ...; $i++; }

but you can't, because while takes an expression as the condition, and
f($i), $i < 10 is not an expression!

>> 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's a syntactic symbol that can be used to combine simpler expressions
in such a way that the result is also, syntactically, an expression. In
PHP, you can't take two expressions (E1) and (E2) and write ((E1), (E2))
to get a new expression - the syntax for expressions simply doesn't
permit the use of ',' as an operator.

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

Because they do.

--
Ben.
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