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Delegator

This library provides three different ways to delegate method calls to an object. The easiest to use is SimpleDelegator. Pass an object to the constructor and all methods supported by the object will be delegated. This object can be changed later.

Going a step further, the top level DelegateClass method allows you to easily setup delegation through class inheritance. This is considerably more flexible and thus probably the most common use for this library.

Finally, if you need full control over the delegation scheme, you can inherit from the abstract class Delegator and customize as needed. (If you find yourself needing this control, have a look at Forwardable which is also in the standard library. It may suit your needs better.)

SimpleDelegator’s implementation serves as a nice example of the use of Delegator:

require 'delegate'

class SimpleDelegator < Delegator
  def __getobj__
    @delegate_sd_obj # return object we are delegating to, required
  end

  def __setobj__(obj)
    @delegate_sd_obj = obj # change delegation object,
                           # a feature we're providing
  end
end

Notes

Be advised, RDoc will not detect delegated methods.

Tempfile

A utility class for managing temporary files. When you create a Tempfile object, it will create a temporary file with a unique filename. A Tempfile objects behaves just like a File object, and you can perform all the usual file operations on it: reading data, writing data, changing its permissions, etc. So although this class does not explicitly document all instance methods supported by File, you can in fact call any File instance method on a Tempfile object.

Synopsis 

require 'tempfile'

file = Tempfile.new('foo')
file.path      # => A unique filename in the OS's temp directory,
               #    e.g.: "/tmp/foo.24722.0"
               #    This filename contains 'foo' in its basename.
file.write("hello world")
file.rewind
file.read      # => "hello world"
file.close
file.unlink    # deletes the temp file

Good practices

Explicit close

When a Tempfile object is garbage collected, or when the Ruby interpreter exits, its associated temporary file is automatically deleted. This means that it’s unnecessary to explicitly delete a Tempfile after use, though it’s a good practice to do so: not explicitly deleting unused Tempfiles can potentially leave behind a large number of temp files on the filesystem until they’re garbage collected. The existence of these temp files can make it harder to determine a new Tempfile filename.

Therefore, one should always call unlink or close in an ensure block, like this:

file = Tempfile.new('foo')
begin
   # ...do something with file...
ensure
   file.close
   file.unlink   # deletes the temp file
end

Tempfile.create { … } exists for this purpose and is more convenient to use. Note that Tempfile.create returns a File instance instead of a Tempfile, which also avoids the overhead and complications of delegation.

Tempfile.create('foo') do |file|
   # ...do something with file...
end

Unlink after creation

On POSIX systems, it’s possible to unlink a file right after creating it, and before closing it. This removes the filesystem entry without closing the file handle, so it ensures that only the processes that already had the file handle open can access the file’s contents. It’s strongly recommended that you do this if you do not want any other processes to be able to read from or write to the Tempfile, and you do not need to know the Tempfile’s filename either.

For example, a practical use case for unlink-after-creation would be this: you need a large byte buffer that’s too large to comfortably fit in RAM, e.g. when you’re writing a web server and you want to buffer the client’s file upload data.

Please refer to unlink for more information and a code example.

Minor notes

Tempfile’s filename picking method is both thread-safe and inter-process-safe: it guarantees that no other threads or processes will pick the same filename.

Tempfile itself however may not be entirely thread-safe. If you access the same Tempfile object from multiple threads then you should protect it with a mutex.

Method

Method objects are created by Object#method, and are associated with a particular object (not just with a class). They may be used to invoke the method within the object, and as a block associated with an iterator. They may also be unbound from one object (creating an UnboundMethod) and bound to another.

class Thing
  def square(n)
    n*n
  end
end
thing = Thing.new
meth  = thing.method(:square)

meth.call(9)                 #=> 81
[ 1, 2, 3 ].collect(&meth)   #=> [1, 4, 9]

[ 1, 2, 3 ].each(&method(:puts)) #=> prints 1, 2, 3

require 'date'
%w[2017-03-01 2017-03-02].collect(&Date.method(:parse))
#=> [#<Date: 2017-03-01 ((2457814j,0s,0n),+0s,2299161j)>, #<Date: 2017-03-02 ((2457815j,0s,0n),+0s,2299161j)>]

Comparable

The Comparable mixin is used by classes whose objects may be ordered. The class must define the <=> operator, which compares the receiver against another object, returning a value less than 0, returning 0, or returning a value greater than 0, depending on whether the receiver is less than, equal to, or greater than the other object. If the other object is not comparable then the <=> operator should return nil. Comparable uses <=> to implement the conventional comparison operators (<, <=, ==, >=, and >) and the method between?.

class StringSorter
  include Comparable

  attr :str
  def <=>(other)
    str.size <=> other.str.size
  end

  def initialize(str)
    @str = str
  end

  def inspect
    @str
  end
end

s1 = StringSorter.new("Z")
s2 = StringSorter.new("YY")
s3 = StringSorter.new("XXX")
s4 = StringSorter.new("WWWW")
s5 = StringSorter.new("VVVVV")

s1 < s2                       #=> true
s4.between?(s1, s3)           #=> false
s4.between?(s3, s5)           #=> true
[ s3, s2, s5, s4, s1 ].sort   #=> [Z, YY, XXX, WWWW, VVVVV]

What’s Here

Module Comparable provides these methods, all of which use method <=>:

Enumerable

What’s Here

Module Enumerable provides methods that are useful to a collection class for:

Methods for Querying

These methods return information about the Enumerable other than the elements themselves:

Methods for Fetching

These methods return entries from the Enumerable, without modifying it:

Leading, trailing, or all elements:

Minimum and maximum value elements:

Groups, slices, and partitions:

Methods for Searching and Filtering

These methods return elements that meet a specified criterion:

Methods for Sorting

These methods return elements in sorted order:

Methods for Iterating

Other Methods

Usage

To use module Enumerable in a collection class:

Example:

class Foo
  include Enumerable
  def each
    yield 1
    yield 1, 2
    yield
  end
end
Foo.new.each_entry{ |element| p element }

Output:

1
[1, 2]
nil

Enumerable in Ruby Classes

These Ruby core classes include (or extend) Enumerable:

These Ruby standard library classes include Enumerable:

Virtually all methods in Enumerable call method #each in the including class:

About the Examples

The example code snippets for the Enumerable methods:

Fiddle

A libffi wrapper for Ruby.

Description

Fiddle is an extension to translate a foreign function interface (FFI) with ruby.

It wraps libffi, a popular C library which provides a portable interface that allows code written in one language to call code written in another language.

Example

Here we will use Fiddle::Function to wrap floor(3) from libm

require 'fiddle'

libm = Fiddle.dlopen('/lib/libm.so.6')

floor = Fiddle::Function.new(
  libm['floor'],
  [Fiddle::TYPE_DOUBLE],
  Fiddle::TYPE_DOUBLE
)

puts floor.call(3.14159) #=> 3.0

FileTest

FileTest implements file test operations similar to those used in File::Stat. It exists as a standalone module, and its methods are also insinuated into the File class. (Note that this is not done by inclusion: the interpreter cheats).

Forwardable

The Forwardable module provides delegation of specified methods to a designated object, using the methods def_delegator and def_delegators.

For example, say you have a class RecordCollection which contains an array @records. You could provide the lookup method record_number(), which simply calls [] on the @records array, like this:

require 'forwardable'

class RecordCollection
  attr_accessor :records
  extend Forwardable
  def_delegator :@records, :[], :record_number
end

We can use the lookup method like so:

r = RecordCollection.new
r.records = [4,5,6]
r.record_number(0)  # => 4

Further, if you wish to provide the methods size, <<, and map, all of which delegate to @records, this is how you can do it:

class RecordCollection # re-open RecordCollection class
  def_delegators :@records, :size, :<<, :map
end

r = RecordCollection.new
r.records = [1,2,3]
r.record_number(0)   # => 1
r.size               # => 3
r << 4               # => [1, 2, 3, 4]
r.map { |x| x * 2 }  # => [2, 4, 6, 8]

You can even extend regular objects with Forwardable.

my_hash = Hash.new
my_hash.extend Forwardable              # prepare object for delegation
my_hash.def_delegator "STDOUT", "puts"  # add delegation for STDOUT.puts()
my_hash.puts "Howdy!"

Another example

You could use Forwardable as an alternative to inheritance, when you don’t want to inherit all methods from the superclass. For instance, here is how you might add a range of Array instance methods to a new class Queue:

class Queue
  extend Forwardable

  def initialize
    @q = [ ]    # prepare delegate object
  end

  # setup preferred interface, enq() and deq()...
  def_delegator :@q, :push, :enq
  def_delegator :@q, :shift, :deq

  # support some general Array methods that fit Queues well
  def_delegators :@q, :clear, :first, :push, :shift, :size
end

q = Thread::Queue.new
q.enq 1, 2, 3, 4, 5
q.push 6

q.shift    # => 1
while q.size > 0
  puts q.deq
end

q.enq "Ruby", "Perl", "Python"
puts q.first
q.clear
puts q.first

This should output:

2
3
4
5
6
Ruby
nil

Notes

Be advised, RDoc will not detect delegated methods.

forwardable.rb provides single-method delegation via the def_delegator and def_delegators methods. For full-class delegation via DelegateClass, see delegate.rb.

MakeMakefile

mkmf.rb is used by Ruby C extensions to generate a Makefile which will correctly compile and link the C extension to Ruby and a third-party library.

Observable

The Observer pattern (also known as publish/subscribe) provides a simple mechanism for one object to inform a set of interested third-party objects when its state changes.

Mechanism

The notifying class mixes in the Observable module, which provides the methods for managing the associated observer objects.

The observable object must:

An observer subscribes to updates using Observable#add_observer, which also specifies the method called via notify_observers. The default method for notify_observers is update.

Example

The following example demonstrates this nicely. A Ticker, when run, continually receives the stock Price for its @symbol. A Warner is a general observer of the price, and two warners are demonstrated, a WarnLow and a WarnHigh, which print a warning if the price is below or above their set limits, respectively.

The update callback allows the warners to run without being explicitly called. The system is set up with the Ticker and several observers, and the observers do their duty without the top-level code having to interfere.

Note that the contract between publisher and subscriber (observable and observer) is not declared or enforced. The Ticker publishes a time and a price, and the warners receive that. But if you don’t ensure that your contracts are correct, nothing else can warn you.

require "observer"

class Ticker          ### Periodically fetch a stock price.
  include Observable

  def initialize(symbol)
    @symbol = symbol
  end

  def run
    last_price = nil
    loop do
      price = Price.fetch(@symbol)
      print "Current price: #{price}\n"
      if price != last_price
        changed                 # notify observers
        last_price = price
        notify_observers(Time.now, price)
      end
      sleep 1
    end
  end
end

class Price           ### A mock class to fetch a stock price (60 - 140).
  def self.fetch(symbol)
    60 + rand(80)
  end
end

class Warner          ### An abstract observer of Ticker objects.
  def initialize(ticker, limit)
    @limit = limit
    ticker.add_observer(self)
  end
end

class WarnLow < Warner
  def update(time, price)       # callback for observer
    if price < @limit
      print "--- #{time.to_s}: Price below #@limit: #{price}\n"
    end
  end
end

class WarnHigh < Warner
  def update(time, price)       # callback for observer
    if price > @limit
      print "+++ #{time.to_s}: Price above #@limit: #{price}\n"
    end
  end
end

ticker = Ticker.new("MSFT")
WarnLow.new(ticker, 80)
WarnHigh.new(ticker, 120)
ticker.run

Produces:

Current price: 83
Current price: 75
--- Sun Jun 09 00:10:25 CDT 2002: Price below 80: 75
Current price: 90
Current price: 134
+++ Sun Jun 09 00:10:25 CDT 2002: Price above 120: 134
Current price: 134
Current price: 112
Current price: 79
--- Sun Jun 09 00:10:25 CDT 2002: Price below 80: 79

Usage with procs

The #notify_observers method can also be used with +proc+s by using the :call as func parameter.

The following example illustrates the use of a lambda:

require 'observer'

class Ticker
  include Observable

  def run
    # logic to retrieve the price (here 77.0)
    changed
    notify_observers(77.0)
  end
end

ticker = Ticker.new
warner = ->(price) { puts "New price received: #{price}" }
ticker.add_observer(warner, :call)
ticker.run

Enumerator::Producer

Producer

IO::EWOULDBLOCKWaitReadable

exception to wait for reading by EWOULDBLOCK. see IO.select.

IO::EWOULDBLOCKWaitWritable

exception to wait for writing by EWOULDBLOCK. see IO.select.

Net::HTTPNotModified

Response class for Not Modified responses (status code 304).

Indicates that the resource has not been modified since the version specified by the request headers.

References:

Prism::AliasGlobalVariableNode

Represents the use of the ‘alias` keyword to alias a global variable.

alias $foo $bar
^^^^^^^^^^^^^^^

Prism::AliasMethodNode

Represents the use of the ‘alias` keyword to alias a method.

alias foo bar
^^^^^^^^^^^^^

Prism::BlockLocalVariableNode

Represents a block local variable.

a { |; b| }
       ^

Prism::ClassVariableAndWriteNode

Represents the use of the ‘&&=` operator for assignment to a class variable.

@@target &&= value
^^^^^^^^^^^^^^^^^^

Prism::ClassVariableOperatorWriteNode

Represents assigning to a class variable using an operator that isn’t ‘=`.

@@target += value
^^^^^^^^^^^^^^^^^

Prism::ClassVariableOrWriteNode

Represents the use of the ‘||=` operator for assignment to a class variable.

@@target ||= value
^^^^^^^^^^^^^^^^^^

Prism::ClassVariableReadNode

Represents referencing a class variable.

@@foo
^^^^^

Prism::ClassVariableTargetNode

Represents writing to a class variable in a context that doesn’t have an explicit value.

@@foo, @@bar = baz
^^^^^  ^^^^^

Prism::ClassVariableWriteNode

Represents writing to a class variable.

@@foo = 1
^^^^^^^^^

Prism::EmbeddedVariableNode

Represents an interpolated variable.

"foo #@bar"
     ^^^^^
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