When writing libraries for other programs to use
is it better to include any outside requirements
within the Class definition or outside it? i.e.
[1]
require “foo”
Class Bar
end
or
[2]
Class Bar
require “foo”
end
If my understanding is correct, 2 is politer in that you
don’t pollute the global namespace with the class defines in
foo. But I most often see [1] in existing ruby libraries. Is
there more to this than I understand?
–
[1] and [2] have the same effect for ruby interpreter at all because
namespace will not be nested by require' or load’.
A human may get a little different sense from them: [1] says this library or script requires "foo"' whereas [2] says this definition of
class Bar requires “foo”'. But this is a problem of taste or calture.
[1] can list all required libraries on the top of a program but [2]
doesn’t. That may helps the reader expect something to use. On the
other hand, [2] points what feature depends on the libraries but [1]
doesn’t. That may be helpful to track the dependency (hopefully
correct).
There is another story if `require’ is put in def statement. Inside
of def would not be evaluated until the method is invoked. So require
in def can postpone loading a library file until really needed. That
may improve average performance in some cases.
– Gotoken
At Fri, 2 Aug 2002 07:33:03 +0900, bbense+comp.lang.ruby.Aug.01.02@telemark.stanford.edu wrote:
When writing libraries for other programs to useis it better to include any outside requirements
within the Class definition or outside it? i.e.[1]
require “foo”Class Bar
end
or
[2]
Class Bar
require “foo”end
…and make debugging harder. But aren’t we all doing unit testing? 
-billy.
On Fri, Aug 02, 2002 at 08:35:32AM +0900, GOTO Kentaro wrote:
There is another story if `require’ is put in def statement. Inside
of def would not be evaluated until the method is invoked. So require
in def can postpone loading a library file until really needed. That
may improve average performance in some cases.
–
Meisterbohne Söflinger Straße 100 Tel: +49-731-399 499-0
eLösungen 89077 Ulm Fax: +49-731-399 499-9
In article 200208012333.g71NXWiG001635@miso.k.notwork.org,
When writing libraries for other programs to useis it better to include any outside requirements
within the Class definition or outside it? i.e.[1]
require “foo”Class Bar
end
or
[2]
Class Bar
require “foo”end
[1] and [2] have the same effect for ruby interpreter at all because
namespace will not be nested byrequire' orload’.
[1]- It’s a command not a preprocessor.
GOTO Kentaro gotoken@notwork.org wrote:
At Fri, 2 Aug 2002 07:33:03 +0900, >bbense+comp.lang.ruby.Aug.01.02@telemark.stanford.edu wrote:
–
By the way, unit testing is big fun but useful only if that testing is
done thoroughgoingly. For example, a bug by require-in-def would be
missed detecting if the method is skipped in a test. Now, I wrote a
coverage testrunner, subclass of Test::Unit::UI::CONSOLE::TestRunner:
http://www.notwork.org/~gotoken/ruby/p/as-is/testrunner_coverage.rb
This is very ad hoc one but I found some missing tests by this toy.
Test first? I know I know… but I often forget it 
More sophisticated coverage test may help the unit test to complete? (#)
(#) NaHi told me this idea, not mine.
At Fri, 2 Aug 2002 18:33:59 +0900, Philipp Meier wrote:
On Fri, Aug 02, 2002 at 08:35:32AM +0900, GOTO Kentaro wrote:
There is another story if `require’ is put in def statement. Inside
of def would not be evaluated until the method is invoked. So require
in def can postpone loading a library file until really needed. That
may improve average performance in some cases.…and make debugging harder. But aren’t we all doing unit testing?
Yes. require doesn’t “insert” code there. require only loads a
library, i.e., reads and evaluates that always in the top level
context unless already loaded.
A Ruby code has identical semantics regardless of require’d or
directly invoked:
% cat ./usee.rb
def a(arg)
[FILE, arg, self]
end
p [1, a(FILE)]
% ruby ./usee.rb
[1, [“./usee.rb”, “./usee.rb”, main]]
% cat ./user.rb
class C
require “usee”
p [2, a(FILE)]
end
require “usee”
p [3, a(FILE)]
p [4, C.public_methods.include?(“a”)]
p [5, Object.private_methods.include?(“a”)]
% ruby ./user.rb
[1, [“./usee.rb”, “./usee.rb”, main]]
[2, [“./usee.rb”, “./user.rb”, C]]
[3, [“./usee.rb”, “./user.rb”, main]]
[4, false]
[5, true]
In other word, Ruby’s require is similar to Emacs-Lisp’s require,
which never loads a library twice and doesn’t change the meaning of a
library to be loaded.
– Gotoken
At Sat, 3 Aug 2002 03:14:44 +0900, bbense+comp.lang.ruby.Aug.02.02@telemark.stanford.edu wrote:
[1] and [2] have the same effect for ruby interpreter at all because
namespace will not be nested byrequire' orload’.
- So require is not just a “smart” include, but something that
works at the language level[1].