# Warnings on assignments in conditionals?

**URL:** <https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665>\
**Category:** ruby-talk\
**Created:** [13 January 2004 17:40 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665 "2004-01-13T17:40:16Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![David\_Heinemeier\_Ha2](https://avatars.discourse-cdn.com/v4/letter/d/fbc32d/32.png) [@David\_Heinemeier\_Ha2](https://rubytalk.org/u/David_Heinemeier_Ha2)\
**Post date:** [13 January 2004 17:40 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/1 "2004-01-13T17:40:16Z")

</div>

I consider the following statements to be perfectly legit (although  
perhaps slightly ambigious) and Ruby does obey, but throws this  
mandating warning. Am I just being paranoid or is Ruby forcing a style  
upon me :)?

irb(main):008:0\> if a = 1 then true else false end  
(irb):8: warning: found = in conditional, should be ==  
=\> true  
irb(main):009:0\> a  
=\> 1

irb(main):010:0\> if a = nil then true else false end  
(irb):10: warning: found = in conditional, should be ==  
=\> false  
irb(main):011:0\> a  
=\> nil

> **···**
>
> –  
> David Heinemeier Hansson.  
> [http://www.loudthinking.com/](http://www.loudthinking.com/) – Broadcasting Brain

---

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**Author:** ![Lyle\_Johnson6](https://avatars.discourse-cdn.com/v4/letter/l/bb73d2/32.png) [@Lyle\_Johnson6](https://rubytalk.org/u/Lyle_Johnson6)\
**Post date:** [13 January 2004 17:56 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/2 "2004-01-13T17:56:36Z")

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David Heinemeier Hansson wrote:

> I consider the following statements to be perfectly legit (although  
> perhaps slightly ambigious) and Ruby does obey, but throws this  
> mandating warning. Am I just being paranoid or is Ruby forcing a style  
> upon me :)?

A single equals sign does assignment, so a statement like:

```
 if a = 1 then true else false end

```

assigns the value 1 to ‘a’, and then evaluates the “truthfulness” of  
‘a’. In Ruby, only ‘false’ and and ‘nil’ evaluate to false, so this  
statement will _always_ evaluate to true (i.e. because ‘a’ is 1, and 1  
is true).

If you’re wanting to check whether the current value of ‘a’ is 1, you  
need to use two equals signs instead, i.e.

```
 if a == 1 then true else false end

```

This statement doesn’t change the value of ‘a’ (as the previous  
statement did). It just compares its current value against another value  
(1) and returns true if they are equal.

Apologies in advance if you already understand this distinction, but it  
is one that has tripped many a programmer, even those who should know  
better 😉 If you indeed mean to assign the value to ‘a’ (as in the first  
example), you can probably avoid the warning from Ruby by breaking this  
into two lines, e.g.

```
 a = 1
 if a then true else false end

```

Hope this helps,

Lyle

---

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**Author:** ![Martin\_S\_Weber](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@Martin\_S\_Weber](https://rubytalk.org/u/Martin_S_Weber)\
**Post date:** [13 January 2004 18:09 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/3 "2004-01-13T18:09:58Z")

</div>

Oops, accidentally replied in private:

> I consider the following statements to be perfectly legit (although  
> perhaps slightly ambigious) and Ruby does obey, but throws this  
> mandating warning. Am I just being paranoid or is Ruby forcing a style  
> upon me :)?

It is. The ‘gcc’ style… an additional pair of parens around the  
expression et voila (funny enough, you need two)

irb(main):001:0\> if a = 1 then true else false end  
(irb):1: warning: found = in conditional, should be ==  
=\> true  
irb(main):002:0\> if (a=1) then true else false end  
(irb):2: warning: found = in conditional, should be ==  
=\> true  
irb(main):003:0\> if ((a=1)) then true else false end  
=\> true

Regards,

-Martin

…to which David replied:

> > It is. The ‘gcc’ style… an additional pair of parens around the  
> > expression et voila (funny enough, you need two)
> 
> Pretty interesting. Anyone has the full story on why?
> 
> / David

Sorry.

-Martin

> **···**
>
> On Wed, Jan 14, 2004 at 02:40:16AM +0900, David Heinemeier Hansson wrote:

---

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**Author:** ![Ara.T.Howard](https://avatars.discourse-cdn.com/v4/letter/a/a8b319/32.png) [@Ara.T.Howard](https://rubytalk.org/u/Ara.T.Howard)\
**Post date:** [13 January 2004 20:06 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/4 "2004-01-13T20:06:42Z")

</div>

> Date: Wed, 14 Jan 2004 02:40:16 +0900  
> From: David Heinemeier Hansson [david@loudthinking.com](mailto:david@loudthinking.com)  
> Newsgroups: comp.lang.ruby  
> Subject: Warnings on assignments in conditionals?
> 
> I consider the following statements to be perfectly legit (although  
> perhaps slightly ambigious) and Ruby does obey, but throws this  
> mandating warning. Am I just being paranoid or is Ruby forcing a style  
> upon me :)?
> 
> irb(main):008:0\> if a = 1 then true else false end  
> irb(main):008:0\> if((a = 1)) then true else false end

> (irb):8: warning: found = in conditional, should be ==  
> =\> true  
> irb(main):009:0\> a  
> =\> 1
> 
> irb(main):010:0\> if a = nil then true else false end  
> irb(main):010:0\> if((a = nil)) then true else false end

> ## (irb):10: warning: found = in conditional, should be == =\> false irb(main):011:0\> a =\> nil
> 
> David Heinemeier Hansson.  
> [http://www.loudthinking.com/](http://www.loudthinking.com/) – Broadcasting Brain

-a

> **···**
>
> ## On Wed, 14 Jan 2004, David Heinemeier Hansson wrote:
> 
> ATTN: please update your address books with address below!
> 
> ===============================================================================
> 
> > EMAIL :: Ara [dot] T [dot] Howard [at] noaa [dot] gov  
> > PHONE :: 303.497.6469  
> > ADDRESS :: E/GC2 325 Broadway, Boulder, CO 80305-3328  
> > STP :: [Solar-Terrestrial Physics Data | NCEI](http://www.ngdc.noaa.gov/stp/)  
> > NGDC :: [http://www.ngdc.noaa.gov/](http://www.ngdc.noaa.gov/)  
> > NESDIS :: [http://www.nesdis.noaa.gov/](http://www.nesdis.noaa.gov/)  
> > NOAA :: [http://www.noaa.gov/](http://www.noaa.gov/)  
> > US DOC :: [http://www.commerce.gov/](http://www.commerce.gov/)
> > 
> > The difference between art and science is that science is what we  
> > understand well enough to explain to a computer.  
> > Art is everything else.  
> > – Donald Knuth, “Discover”
> > 
> > /bin/sh -c ‘for l in ruby perl;do $l -e “print "\x3a\x2d\x29\x0a"”;done’  
> > ===============================================================================

---

<div class="post-metadata">

**Author:** ![oinkoink](https://avatars.discourse-cdn.com/v4/letter/o/8e8cbc/32.png) [@oinkoink](https://rubytalk.org/u/oinkoink)\
**Post date:** [14 January 2004 19:11 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/5 "2004-01-14T19:11:39Z")

</div>

David Heinemeier Hansson [david@loudthinking.com](mailto:david@loudthinking.com) wrote in message news:[8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com](mailto:8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com)…

> I consider the following statements to be perfectly legit (although  
> perhaps slightly ambigious) and Ruby does obey, but throws this  
> mandating warning. Am I just being paranoid or is Ruby forcing a style  
> upon me :)?
> 
> irb(main):008:0\> if a = 1 then true else false end  
> (irb):8: warning: found = in conditional, should be ==  
> =\> true  
> irb(main):009:0\> a  
> =\> 1
> 
> irb(main):010:0\> if a = nil then true else false end  
> (irb):10: warning: found = in conditional, should be ==  
> =\> false  
> irb(main):011:0\> a  
> =\> nil

But this C idiom really doesn’t make much sense in Ruby, since  
in Ruby 0 is true in a boolean context. You might want to say  
something like:  
if not (a = c).nil? then foo else bar end  
but what you have is almost certainly either an error or at least  
stylistically dubious. So yes, I guess Ruby is forcing a style on  
you. I think that if you really want something like this, the Ruby  
way would be to define a method ‘true?’ for objects:  
class Object  
def true?  
if nil? or self == false then return false end  
true  
end  
def false?  
not true?  
end  
end

then write:  
if (a = c).true? then foo else bar end

Oinkful Regards, Bret

---

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**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\
**Post date:** [14 January 2004 21:36 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/6 "2004-01-14T21:36:37Z")

</div>

“David Heinemeier Hansson” [david@loudthinking.com](mailto:david@loudthinking.com) schrieb im Newsbeitrag  
[news:8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com](mailto:news:8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com)…

> I consider the following statements to be perfectly legit (although  
> perhaps slightly ambigious) and Ruby does obey, but throws this  
> mandating warning. Am I just being paranoid or is Ruby forcing a style  
> upon me :)?
> 
> irb(main):008:0\> if a = 1 then true else false end  
> (irb):8: warning: found = in conditional, should be ==  
> =\> true  
> irb(main):009:0\> a  
> =\> 1
> 
> irb(main):010:0\> if a = nil then true else false end  
> (irb):10: warning: found = in conditional, should be ==  
> =\> false  
> irb(main):011:0\> a  
> =\> nil

Just a side remark: assignment in conditional is only used in loops. “if”  
never needs this. You can always put it onto two lines even gaining  
readability:

a = 1  
if a then …

Besides of that you can do

a = 1 and …

This will look familiar to P\*rl users.

You only really need it in situations like this:

while ( line = gets )  
…  
end

Cheers

```
robert

```

---

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**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\
**Post date:** [15 January 2004 09:11 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/7 "2004-01-15T09:11:36Z")

</div>

“Bret Jolly” [oinkoink+unet@rexx.com](mailto:oinkoink+unet@rexx.com) schrieb im Newsbeitrag  
[news:7e7131a1.0401141110.d5fa65a@posting.google.com](mailto:news:7e7131a1.0401141110.d5fa65a@posting.google.com)…

> David Heinemeier Hansson [david@loudthinking.com](mailto:david@loudthinking.com) wrote in message  
> news:[8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com](mailto:8609BD15-45EF-11D8-A416-000A958E6254@loudthinking.com)…
> 
> > I consider the following statements to be perfectly legit (although  
> > perhaps slightly ambigious) and Ruby does obey, but throws this  
> > mandating warning. Am I just being paranoid or is Ruby forcing a style  
> > upon me :)?
> > 
> > irb(main):008:0\> if a = 1 then true else false end  
> > (irb):8: warning: found = in conditional, should be ==  
> > =\> true  
> > irb(main):009:0\> a  
> > =\> 1
> > 
> > irb(main):010:0\> if a = nil then true else false end  
> > (irb):10: warning: found = in conditional, should be ==  
> > =\> false  
> > irb(main):011:0\> a  
> > =\> nil
> 
> But this C idiom really doesn’t make much sense in Ruby, since  
> in Ruby 0 is true in a boolean context. You might want to say  
> something like:  
> if not (a = c).nil? then foo else bar end  
> but what you have is almost certainly either an error or at least  
> stylistically dubious. So yes, I guess Ruby is forcing a style on  
> you. I think that if you really want something like this, the Ruby  
> way would be to define a method ‘true?’ for objects:  
> class Object  
> def true?  
> if nil? or self == false then return false end  
> true  
> end  
> def false?  
> not true?  
> end  
> end
> 
> then write:  
> if (a = c).true? then foo else bar end

_shudder_ You’re not serious, are you? And if so, why didn’t you define  
them like this:

class Object  
def true?; self; end  
def false?; not self; end  
end

Cheers

```
robert

```

---

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**Author:** ![oinkoink](https://avatars.discourse-cdn.com/v4/letter/o/8e8cbc/32.png) [@oinkoink](https://rubytalk.org/u/oinkoink)\
**Post date:** [15 January 2004 18:31 UTC](https://rubytalk.org/t/warnings-on-assignments-in-conditionals/9665/8 "2004-01-15T18:31:35Z")

</div>

“Robert Klemme” [bob.news@gmx.net](mailto:bob.news@gmx.net) wrote in message news:[bu5l86$dmuo3$1@ID-52924.news.uni-berlin.de](mailto:bu5l86$dmuo3$1@ID-52924.news.uni-berlin.de)…

> “Bret Jolly” [oinkoink+unet@rexx.com](mailto:oinkoink+unet@rexx.com) schrieb im Newsbeitrag  
> [stuff]

> _shudder_ You’re not serious, are you? And if so, why didn’t you define  
> them like this:

> class Object  
> def true?; self; end  
> def false?; not self; end  
> end

Yes, that’s much better.  
Oinkful and Blushing Regards, Bret