ChatGPT解决这个技术问题 Extra ChatGPT

What is the difference between include and require in Ruby?

My question is similar to "What is the difference between include and extend in Ruby?".

What's the difference between require and include in Ruby? If I just want to use the methods from a module in my class, should I require it or include it?

For what it's worth, here are links to the community documentation for require and include, and also relevant, Module#append_features.

s
stkent

What's the difference between "include" and "require" in Ruby? Answer: The include and require methods do very different things. The require method does what include does in most other programming languages: run another file. It also tracks what you've required in the past and won't require the same file twice. To run another file without this added functionality, you can use the load method. The include method takes all the methods from another module and includes them into the current module. This is a language-level thing as opposed to a file-level thing as with require. The include method is the primary way to "extend" classes with other modules (usually referred to as mix-ins). For example, if your class defines the method "each", you can include the mixin module Enumerable and it can act as a collection. This can be confusing as the include verb is used very differently in other languages.

Source

So if you just want to use a module, rather than extend it or do a mix-in, then you'll want to use require.

Oddly enough, Ruby's require is analogous to C's include, while Ruby's include is almost nothing like C's include.


In fact C's include, doesn't load a file as require do, but instead replace the #include line, by the content of the file. Included files don't have to be 'header' and #include don't have to be at the beginning of file but can be anywhere, like in class or even a method definition. This means you can do mixin in C++ by writting some methods in a file and include it in the code of a class, exactly has you would do in ruby. So they are not that far, even though it's indeed not a common practice in C's.
This answer could benefit by including examples.
mb14's comment implies this, but it bears stating explicitly: contrary to what the answer says, require does not "run" a file, but rather loads it as though it were part of the containing file. This might seem like semantic nitpicking but actually it's a rather important difference.
@LonnyEachus: This is wrong. require simply runs the file. Period. In particular, this means that if you put the require call inside a class declaration, the code in the file will not become a part of that class, if you put the require call inside a method definition, the code in the file will not become a part of that method, if you put the require call inside a module declaration, the code in the file will not become part of that module, and so on and so forth. It doesn't even become part of the file the require call is in. There's plenty of question here on Stack Overflow that are …
@GregSchmit: include in Ruby is simply inheritance. class C; include M end makes M the superclass of C and the (former) superclass of C the superclass of M. I don't think that C's include works via inheritance, I think it is simple textual/lexical substitution.
A
Andrei

If you're using a module, that means you're bringing all the methods into your class. If you extend a class with a module, that means you're "bringing in" the module's methods as class methods. If you include a class with a module, that means you're "bringing in" the module's methods as instance methods.

EX:

 module A
   def say
     puts "this is module A"
   end
 end

 class B
   include A
 end

 class C
   extend A
 end

B.say => undefined method 'say' for B:Class

B.new.say => this is module A

C.say => this is module A

C.new.say => undefined method 'say' for C:Class


I think this does not answer the question, but it is what I was looking for =)
This doesn't actually answer the question of what the differences between require and include are.
J
Jonathan Fretheim

From the Metaprogramming Ruby book,

The require() method is quite similar to load(), but it’s meant for a different purpose. You use load() to execute code, and you use require() to import libraries.


Upvote for not comparing to another language in your answer :)
Down vote for not providing an answer in the context of the question: "If I just want to use the methods from a module in my class?"
I
Iulian Onofrei

Ruby require is more like "include" in other languages (such as C). It tells Ruby that you want to bring in the contents of another file. Similar mechanisms in other languages are: using directive in C#. import in Java.

using directive in C#.

import in Java.

Ruby include is an object-oriented inheritance mechanism used for mixins.

There is a good explanation here:

[The] simple answer is that require and include are essentially unrelated. "require" is similar to the C include, which may cause newbie confusion. (One notable difference is that locals inside the required file "evaporate" when the require is done.) The Ruby include is nothing like the C include. The include statement "mixes in" a module into a class. It's a limited form of multiple inheritance. An included module literally bestows an "is-a" relationship on the thing including it.

Emphasis added.


Module import is not that like file inclusion, as it has nothing necessarily to do with the external source representation of the program. It is more like the include here. Namespaces, packages and class-typed objects can all be treated as specialized environments which hold name bindings in general. (Consider these differences and Kernel's $import!. Also notes Racket's environments are implemented in namespaces.)
c
cizixs

From Programming Ruby 1.9

We’ll make a couple of points about the include statement before we go on. First, it has nothing to do with files. C programmers use a preprocessor directive called #include to insert the contents of one file into another during compilation. The Ruby include statement simply makes a reference to a module. If that module is in a separate file, you must use require (or its less commonly used cousin, load) to drag that file in before using include. Second, a Ruby include does not simply copy the module’s instance methods into the class. Instead, it makes a reference from the class to the included module. If multiple classes include that module, they’ll all point to the same thing. If you change the definition of a method within a module, even while your program is running, all classes that include that module will exhibit the new behavior.


B
Boris Stitnicky

Have you ever tried to require a module? What were the results? Just try:

MyModule = Module.new
require MyModule # see what happens

Modules cannot be required, only included!


The assertion here is not correct. Modules can be required. And anyone running the above code will find that they receive the same result (TypeError) if the word Module is changed to Class.
V
Vaishali Venkatesan

'Load'- inserts a file's contents.(Parse file every time the file is being called)

'Require'- inserts a file parsed content.(File parsed once and stored in memory)

'Include'- includes the module into the class and can use methods inside the module as class's instance method

'Extend'- includes the module into the class and can use methods inside the module as class method


S
Sanket

Include When you Include a module into your class as shown below, it’s as if you took the code defined within the module and inserted it within the class, where you ‘include’ it. It allows the ‘mixin’ behavior. It’s used to DRY up your code to avoid duplication, for instance, if there were multiple classes that would need the same code within the module.

Load The load method is almost like the require method except it doesn’t keep track of whether or not that library has been loaded. So it’s possible to load a library multiple times and also when using the load method you must specify the “.rb” extension of the library file name.

Require The require method allows you to load a library and prevents it from being loaded more than once. The require method will return ‘false’ if you try to load the same library after the first time. The require method only needs to be used if library you are loading is defined in a separate file, which is usually the case.

You can prefer this http://ionrails.com/2009/09/19/ruby_require-vs-load-vs-include-vs-extend/


A
Awais Shafqat

Below are few basic differences between require and include:

Require:

Require reads the file from the file system, parses it, saves to the memory and runs it in a given place which means if you will even change anything while the script is running than that change will not reflect. We require file by name, not by module name. It is typically used for libraries and extensions.

Include:

When you include a module into your class it behaves as if you took the code defined in your module and inserted it in your class. We include module name, not the file name. It is typically used to dry up the code and to remove duplication in the code.


C
Caleb Kleveter
require(name)

It will return bolean true/false

The name which is passed as parameter to the require, ruby will try to find the source file with that name in your load path. The require method will return ‘false’ if you try to load the same library after the first time. The require method only needs to be used if library you are loading is defined in a separate file. So it keeps track of whether that library was already loaded or not.

include module_name

Suppose if you have some methods that you need to have in two different classes. Then you don't have to write them in both the classes. Instead what you can do is, define it in module. And then include this module in other classes. It is provided by Ruby just to ensure DRY principle. It’s used to DRY up your code to avoid duplication