# Require, load and include --- what's the difference? **URL:** \ **Category:** Ruby\ **Created:** [December 17, 2006, 6:20pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651 "2006-12-17T18:20:38Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 6:20pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/1 "2006-12-17T18:20:38Z")
Hello, I’m browsing through some code, trying to familiarize myself with the language (I have a C++ background, with only a #include), and I realize that there are 3 calls that I’m trying to wrap my head around. Here’s my stab: Require – seems to include another file to gain access to other classes, modules, and global data. This seems to be equivalent to a C++ include, with inclusion guards Load – seems to be the same as require, but will actually reload the data every time it is called, where require will load once and cache the file. This seems to be equivalent to C++ include, with out inclusion guards. Include – seems to include a module name from a pre-determined path, but not classes (unless encapsulated within a module). Would this be similar to a C++ namespace being given the include directory at compile time? So a couple of things here, are my understandings of the 3 methods close, if not, could someone please expand on them. The other is what’s the advantage of include vs require? I mean, why would I include a module, rather than require it’s filename? I’ve read through the RDocs, but I still don’t seem to understand. I hope this post makes sense, let me know if I need to clarify. Thanks Matt ---
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 6:52pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/2 "2006-12-17T18:52:45Z")
On 12/17/06, matt [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > include, with inclusion guards > Right > Load – seems to be the same as require, but will actually reload the > data every time it is called, where require will load once and cache the > file. This seems to be equivalent to C++ include, with out inclusion > guards. Right > Include – seems to include a module name from a pre-determined path, > but not classes (unless encapsulated within a module). Would this be > similar to a C++ namespace being given the include directory at compile > time? include mixes in a module, so the methods defined on the module become instance methods on the class. module Foo def foo; “foo”; end end class Boring include Foo end Boring.new.foo =\> “foo” > So a couple of things here, are my understandings of the 3 methods > close, if not, could someone please expand on them. The other is what’s > the advantage of include vs require? I mean, why would I include a > module, rather than require it’s filename? load and require are for loading a file into your code. include is used to actually enhance an individual object (because a class itself is an object). Pat ---
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 6:56pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/3 "2006-12-17T18:56:47Z")
On 12/17/06, matt [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Hello, Hi, > Load – seems to be the same as require, but will actually reload the > data every time it is called, where require will load once and cache the > file. This seems to be equivalent to C++ include, with out inclusion > guards. Seems fine to me with the difference that #include is evaluated at compile time whereas load, require works at run-time (there is no compile-time in Ruby). > Include – seems to include a module name from a pre-determined path, > but not classes (unless encapsulated within a module). Would this be > similar to a C++ namespace being given the include directory at compile > time? You should see include as the ruby approach to multiple inheritance. Include mix in a class the method defined in the given module. This way you can share methods between different classes. > So a couple of things here, are my understandings of the 3 methods > close, if not, could someone please expand on them. The other is what’s > the advantage of include vs require? I mean, why would I include a > module, rather than require it’s filename? require works on a file. It tells ruby to load a file if it is not already loaded. It is closer to the source shell builtin than the #include cpp directory from my point of view. include adds the methods defined in a module into a class. I hope this can help you. Cheers, ---
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 7:00pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/4 "2006-12-17T19:00:48Z")
I think you’ve got it right. require basically copies and pastes the referenced file into the source, but it only includes classes and modules, I don’t think variables besides instance variables and class variables get imported. include makes it so you don’t have to use the scope resolution operator “::”. It “unwraps” a module is how I like to think of it. ---
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 7:04pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/5 "2006-12-17T19:04:49Z")
On Dec 17, 9:19 am, matt [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Require – seems to include another file to gain access to other > classes, modules, and global data. This seems to be equivalent to a C++ > include, with inclusion guards > > Load – seems to be the same as require, but will actually reload the > data every time it is called, where require will load once and cache the > file. This seems to be equivalent to C++ include, with out inclusion > guards. Basically correct on these two. > Include – seems to include a module name from a pre-determined path, > but not classes (unless encapsulated within a module). Would this be > similar to a C++ namespace being given the include directory at compile > time? > what’s > the advantage of include vs require? I mean, why would I include a > module, rather than require it’s filename? Include doesn’t really have anything to do with files or paths. For instance, the following code could all be in the same file: ## BEGIN Woden:~ jwilger$ irb > > module Foo > > def hello > > “defined in module Foo” > > end > > end > > =\> nil ?\> class Bar > > include Foo > > end > > =\> Bar ?\> x = Bar.new =\> #Bar:0x12a1838 > > x.hello > > =\> “defined in module Foo” ## END When used this way, modules and include are Ruby’s preferred way to implement that which would be achieved via multiple inheritance in some other languages. ---
**Author:** ![matt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a6a055/32.png) [@matt](https://www.ruby-forum.com/u/matt)\ **Post date:** [December 17, 2006, 7:04pm UTC](https://www.ruby-forum.com/t/require-load-and-include-whats-the-difference/79651/6 "2006-12-17T19:04:50Z")
matt wrote: > include, with inclusion guards > > Load – seems to be the same as require, but will actually reload the > data every time it is called, where require will load once and cache the > file. This seems to be equivalent to C++ include, with out inclusion > guards. You got the point. There’s a difference however, as you’re including directly the code and not the header as is done usually in C++. Basically, you’ll only ever need to use require, unless you need some special kind of interaction with the (programmer-)user. > Include – seems to include a module name from a pre-determined path, > but not classes (unless encapsulated within a module). Would this be > similar to a C++ namespace being given the include directory at compile > time? I don’t really understand what you mean about the include directory. Module serves two purposes: namespace separation and mixins. Mixins are Ruby’s version of multiple inheritance: whereas C++ authorize multiple parents for classes, Ruby forbids this, but provides a mechanism for classes that share common capabilities to share code as well. Let’s make this more explicit: Array is a descendant of Object, as are all Ruby classes. Hash is also a descendant of Object. But both share some common capabilities, such as they all provide a collection of Objects you might like to go through. This is where modules come in: both include the Enumerable module, which provides facilities to traverse collections of objects. In C++, the design would be different: class Object {}; class Enumerable {}; class Hash: public Object, Enumerable {}; class Array: public Object, Enumerable {}; In ruby, class Array include Enumerable end class Hash include Enumerable end There you go. > So a couple of things here, are my understandings of the 3 methods > close, if not, could someone please expand on them. The other is what’s > the advantage of include vs require? I mean, why would I include a > module, rather than require it’s filename? You need to require the filename first so that the module is available. Then, you can include it in classes if you need their functionality. Cheers, ``` Vince ```