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Ruby Programming
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Including Other Files

Because Ruby makes it easy to write good, modular code, you'll often find yourself producing small files containing some chunk of self-contained functionality---an interface to x, an algorithm to do y, and so on. Typically, you'll organize these files as class or module libraries.

Having produced these files, you'll want to incorporate them into your new programs. Ruby has two statements that do this.

load "filename.rb"

require "filename"

The load method includes the named Ruby source file every time the method is executed, whereas require loads any given file only once. require has additional functionality: it can load shared binary libraries. Both routines accept relative and absolute paths. If given a relative path (or just a plain name), they'll search every directory in the current load path ($:, discussed on page 140) for the file.

Files loaded using load and require can, of course, include other files, which include other files, and so on. What might not be obvious is that require is an executable statement---it may be inside an if statement, or it may include a string that was just built. The search path can be altered at runtime as well. Just add the directory you want to the string $:.

Since load will include the source unconditionally, you can use it to reload a source file that may have changed since the program began:

5.times do |i|
   File.open("temp.rb","w") { |f|
     f.puts "module Temp\ndef Temp.var() #{i}; end\nend"
   }
   load "temp.rb"
   puts Temp.var
 end
produces:
0
1
2
3
4


Ruby Programming
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