How do you think ruby parses this expression?
a = 1 + b = 2 + c = 4 + d = 8
Originally I thought that operator precedence would result in
a = (1 + b) = (2 + c) = (4 + d) = 8
and since an assignment requires a variable, that would result in a SyntaxError. But instead it seems that everything on the right side of the assignment operator is evaluated first:
a = (1 + (b = (2 + (c = (4 + (d = 8))))))
That had me really puzzled at first but I guess the behavior makes a certain sense, and it's more useful than a syntax error. Ruby's tolerant parser wins again!
Daniel
Daniel DeLorme wrote:
How do you think ruby parses this expression?
a = 1 + b = 2 + c = 4 + d = 8
Per...
http://phrogz.net/ProgrammingRuby/language.html#operatorexpressions
...the + operator has much higher precedence than the assignment
operator. That's interesting that it doesn't parse as you expected.
It's what I would have expected, too.
I think Daniel did not want you to do anything - in fact he seems rather positively amazed. 
(The only thing that comes to mind is thank him for the praise. :-))
Kind regards
robert
···
On 02.01.2007 17:56, Yukihiro Matsumoto wrote:
Hi,
In message "Re: operator precedence of assignment" > on Tue, 2 Jan 2007 22:26:53 +0900, Daniel DeLorme <dan-ml@dan42.com> writes:
>
>How do you think ruby parses this expression?
> a = 1 + b = 2 + c = 4 + d = 8
>
>Originally I thought that operator precedence would result in
> a = (1 + b) = (2 + c) = (4 + d) = 8
>and since an assignment requires a variable, that would result in a SyntaxError. >But instead it seems that everything on the right side of the assignment >operator is evaluated first:
> a = (1 + (b = (2 + (c = (4 + (d = 8))))))
>
>That had me really puzzled at first but I guess the behavior makes a certain >sense, and it's more useful than a syntax error. Ruby's tolerant parser wins again!
Ah, for your information, that surprised me as well. Perhaps bison
generated parser is smarter and eagerer than I expected. I have no
idea what to do.
Hi,
I think Daniel did not want you to do anything - in fact he seems rather
positively amazed.
_That_ made me wonder what I should do.
(The only thing that comes to mind is thank him for the praise. :-))
The praise should go to yacc, not me. 
matz.
···
In message "Re: operator precedence of assignment" on Wed, 3 Jan 2007 02:05:06 +0900, Robert Klemme <shortcutter@googlemail.com> writes:
But *you* chose it, didn't you? So...
robert
···
On 02.01.2007 18:09, Yukihiro Matsumoto wrote:
Hi,
In message "Re: operator precedence of assignment" > on Wed, 3 Jan 2007 02:05:06 +0900, Robert Klemme <shortcutter@googlemail.com> writes:
>I think Daniel did not want you to do anything - in fact he seems rather >positively amazed.
_That_ made me wonder what I should do.
>(The only thing that comes to mind is thank him for the praise. :-))
The praise should go to yacc, not me.