# Placement of require() and missing symbols **URL:** \ **Category:** Ruby\ **Created:** [June 17, 2010, 4:22pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295 "2010-06-17T16:22:43Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:22pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/1 "2010-06-17T16:22:43Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello List, I’m trying to understand the way Ruby resolves symbol names and how the require statement fits in. I’ll start right away with an example, which comes in two files (note the comments): - —%\<— # a.rb: require ‘a/b’ module Foo class Foo::A ``` def do_something() b = Foo::A::B.new b.say ``` end end # a/b.rb: require ‘a’ module Foo class Foo:🅰:B \< Foo::A def say puts “Hello, World” end end end - —\>%— With the above code, I get a “missing symbol” error. Placing the “require ‘a/b’” statement within the Foo::A class remedies it. Now I’m not quite sure why. I know that require() is a statement like puts in regards of its execution time, i.e. there’s no special treatment in some parse/compile/whatever phase before the actual execution begins. As such, it seems logic that I get the missing symbol error with the original code: Foo::A is not defined when the derivation is made, and as such, putting require ‘a/b’ some lines later helps. Am I correct with this explanation? Is there any best practice regarding such a situation? While this example is constructed, I’m trying to create a namespace hierarchy in which a class on top mediates several others that live further below the hiearchy, but don’t derive from it. I’m open for all kinds of suggestions. Thanks alot in advance! ``` Eric ``` -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkwWzmkACgkQhS0drJ3goJJSTwCfZ8mJghOxUeiAyApkQFo7PoBA aT0An0GGVaN2aUIHJo8eMrmra7jS/xsy =uQ4K -----END PGP SIGNATURE----- ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:22pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/2 "2010-06-17T16:22:49Z")
On Mon, Jun 14, 2010 at 7:18 PM, Eric MSP Veith [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’m trying to understand the way Ruby resolves symbol names and how the > require statement fits in. The code is executed in a linear fashion. > - —%\<— > > # a.rb: > > require ‘a/b’ At this point, the code in a/b.rb is read and evaluated. So, jump down to there. > # a/b.rb: > > require ‘a’ > > module Foo > class Foo:🅰:B \< Foo::A This expects Foo::A to exist, but the way you have written you code, with this being required before Foo::A is defined in the a.rb code, it won’t exist yet. > def say > puts “Hello, World” > end > end > end > > - —\>%— > > With the above code, I get a “missing symbol” error. Placing the “require > ‘a/b’” statement within the Foo::A class remedies it. This is because by that time Ruby is aware of the existence of the Foo:A class, so your code in a/b.rb can execute. > Is there any best practice regarding such a situation? While this example is > constructed, I’m trying to create a namespace hierarchy in which a class on > top mediates several others that live further below the hiearchy, but don’t > derive from it. Just move your require statements. If a.rb is defining stuff needed by a/b.rb, but you want a require of a.rb to also load a/b.rb, then put that require somewhere else. It doesn’t have to be in the class definition. You can do that, but were it me, I’d just put it along with any other similar require statements at the end of the file, or at least after the class definition that those files are depending on. Kirk H. Developer Engine Y. ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:26pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/3 "2010-06-17T16:26:23Z")
On Mon, Jun 14, 2010 at 9:18 PM, Eric MSP Veith [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Am I correct with this explanation? > Yes > Is there any best practice regarding such a situation? While this example is > constructed, I’m trying to create a namespace hierarchy in which a class on > top mediates several others that live further below the hiearchy, but don’t > derive from it. > > I’m open for all kinds of suggestions. Have a look at the Module#autoload, and Kernel#autoload methods These can be a useful ‘sword’ when trying to manage requires manually becomes a bit of a gordian knot. – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Github: [rubyredrick (Rick DeNatale) · GitHub](http://github.com/rubyredrick) Twitter: @RickDeNatale WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale) ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:27pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/4 "2010-06-17T16:27:01Z")
On Jun 15, 7:25 am, Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Have a look at the Module#autoload, and Kernel#autoload methods > > These can be a useful ‘sword’ when trying to manage requires manually > becomes a bit of a gordian knot. Yea, well, except for the fact that they are broken. [http://groups.google.com/group/ruby-talk-google/browse\_thread/thread/f981e153fb3fc032/7077b6fe2b483092](http://groups.google.com/group/ruby-talk-google/browse_thread/thread/f981e153fb3fc032/7077b6fe2b483092) ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:27pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/5 "2010-06-17T16:27:03Z")
On Tue, Jun 15, 2010 at 12:25 PM, Eric MSP Veith [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > so there’s no actual best practice regaring require() placement? The best practice is to put it where it makes sense to put it, bearing in mind you might have to read your code again in two years, or someone else might have to read your code. The convention is to put requires at the top of the file because it’s immediately obvious what other libraries the code within the file depends on. But, obviously, you are trying to structure your code and your files in a way that breaks that convention. So, either write your code differently, structure your files differently, or move your requires. If you move your requires, I’d put them outside of the class bodies and method bodies, but as close to the relevant code as is reasonable. You might also consider a comment or note someplace explaining why you are doing things differently. Kirk H. Developer Engine Y. ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:27pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/6 "2010-06-17T16:27:01Z")
Kirk, On Tuesday 15 June 2010, Kirk H. wrote: > Just move your require statements. > […] > I’d just put it along with any other similar require statements > at the end of the file, or at least after the class definition that > those files are depending on. so there’s no actual best practice regaring require() placement? ``` Eric ``` ---
**Author:** ![Eric\_MSP\_Veith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecd19e/32.png) [@Eric\_MSP\_Veith](https://www.ruby-forum.com/u/Eric_MSP_Veith)\ **Post date:** [June 17, 2010, 4:34pm UTC](https://www.ruby-forum.com/t/placement-of-require-and-missing-symbols/190295/7 "2010-06-17T16:34:41Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Rick, Intransition, thanks for your answers! On Tuesday 15 June 2010, Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > Now I’m not quite sure why. I know that require() is a statement like > > puts in regards of its execution time, i.e. there’s no special > > treatment in some parse/compile/whatever phase before the actual > > execution begins. As such, it seems logic that I get the missing symbol > > error with the original code: Foo::A is not defined when the derivation > > is made, and as such, putting require ‘a/b’ some lines later helps. > > > > Am I correct with this explanation? > > Yes Ok, that’s a start. 🙂 I haven’t read a lot of Ruby code so far, but from what I’ve looked at, I could see that require() typically goes at the top of the file. Seems to be some sort of (unwritten?) coding style guideline to me. I’m always hestitant to write code that at seems to be outside of the best practices pathway. So the obvious question is: Am I right with the assumption, that issuing a require statement somewhere within the class or method is not quite a good style? (For a similar reason I’d like to avoid the autoloader, too, besides the problems it has.) If so, I’m quite obviously creating a flawed design. What’s the recommendation in this case? TIA! ``` Eric ``` -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkwXkVUACgkQhS0drJ3goJLapQCeMUgjoqulj4KdqX3gTrQEQAOK 1ukAn0017I/xUy75x8o71C9mrfl+JV70 =2tvl -----END PGP SIGNATURE-----