# Operator precedence of assignment **URL:** \ **Category:** Ruby\ **Created:** [January 2, 2007, 2:27pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951 "2007-01-02T14:27:36Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 2:27pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/1 "2007-01-02T14:27:36Z")
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 ---
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 5:02pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/2 "2007-01-02T17:02:05Z")
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](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. ---
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 5:56pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/3 "2007-01-02T17:56:52Z")
Hi, In message “Re: operator precedence of assignment” on Tue, 2 Jan 2007 22:26:53 +0900, Daniel DeLorme [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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. ``` matz. ``` ---
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 6:06pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/4 "2007-01-02T18:06:56Z")
On 02.01.2007 17:56, Yukihiro M. wrote: > |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. 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 ``` ---
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 10:02pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/5 "2007-01-02T22:02:09Z")
On 02.01.2007 18:09, Yukihiro M. wrote: > |(The only thing that comes to mind is thank him for the praise. :-)) > > The praise should go to yacc, not me. 😉 But _you_ chose it, didn’t you? So… 🙂 ``` robert ``` ---
**Author:** ![Daniel\_DeLorme](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9d8465/32.png) [@Daniel\_DeLorme](https://www.ruby-forum.com/u/Daniel_DeLorme)\ **Post date:** [January 2, 2007, 6:10pm UTC](https://www.ruby-forum.com/t/operator-precedence-of-assignment/80951/6 "2007-01-02T18:10:59Z")
Hi, In message “Re: operator precedence of assignment” on Wed, 3 Jan 2007 02:05:06 +0900, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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. 😉 ``` matz. ```