In Ruby, the command ri is used to access the built-in documentation (also known as “RDoc”) of a library, class, method, or specific topic. ri is an abbreviation for “Ruby Interactive” or “Ruby Index.”
When you run the ri command in the terminal, followed by a class, method, or topic name, you will see the documentation related to that element.
For example, if you run the ri Array command in the terminal, you will see something like this:
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(from ruby core)
------------------------------------------------------------------------
An Array is an ordered, integer-indexed collection of objects, called
elements. Any object (even another array) may be an
array element, and an array can contain objects of different types.
== Array Indexes
Array indexing starts at 0, as in C or Java.
A positive index is an offset from the first element:
* Index 0 indicates the first element.
* Index 1 indicates the second element.
* ...
A negative index is an offset, backwards, from the end of the array:
* Index -1 indicates the last element.
If you run ri Array#each, you will see the documentation for the each method of the Array class.
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ri Array#each
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= Array#each
(from ruby core)
------------------------------------------------------------------------
array.each {|element| ... } -> self
array.each -> Enumerator
------------------------------------------------------------------------
Iterates over array elements.
When a block given, passes each successive array element to the block;
returns self:
a = [:foo, 'bar', 2]
a.each {|element| puts "#{element.class} #{element}" }
Output:
Symbol foo
:
It’s a helpful way to consult Ruby documentation without needing to search in external resources or on the web.
Finding the definition of a method in your Rails application:
Sometimes, you need to find the definition of a method in your Rails application. For instance, you might want to locate the definition of a class or instance method. You can use the source_location method for this purpose. For example:
For instance methods:
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Movie.instance_method(:rating).source_location
# => ["/app/models/movie.rb", 210]
For class methods:
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Movie.singleton_method(:rating).source_location
# => ["/app/models/movie.rb", 21]
You can also use the source method to view the source code of a method.
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Movie.instance_method(:rating).source
# => "def rating\n read_attribute(:rating)\nend\n"
For a better code visualization, you can use the display method.
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Movie.instance_method(:rating).source.display
def rating
read_attribute(:rating)
end
This will be very useful, especially if your code is full of metaprogramming.
Finding the definition of a method in a gem:
To locate the definition of a method in a gem, you can use the bundle open command. For instance, to find the definition of the save method in the activerecord gem:
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bundle open activerecord
This will open the file activerecord/lib/active_record/core.rb in your default text editor. You can then directly search for the save method in the project.