Results for: "Psych"

SystemCallError is the base class for all low-level platform-dependent errors.

The errors available on the current platform are subclasses of SystemCallError and are defined in the Errno module.

File.open("does/not/exist")

raises the exception:

Errno::ENOENT: No such file or directory - does/not/exist

A Symbol object represents a named identifier inside the Ruby interpreter.

You can create a Symbol object explicitly with:

• A symbol literal.

The same Symbol object will be created for a given name or string for the duration of a program’s execution, regardless of the context or meaning of that name. Thus if Fred is a constant in one context, a method in another, and a class in a third, the Symbol :Fred will be the same object in all three contexts.

module One
  class Fred
  end
  $f1 = :Fred
end
module Two
  Fred = 1
  $f2 = :Fred
end
def Fred()
end
$f3 = :Fred
$f1.object_id   #=> 2514190
$f2.object_id   #=> 2514190
$f3.object_id   #=> 2514190

Constant, method, and variable names are returned as symbols:

module One
  Two = 2
  def three; 3 end
  @four = 4
  @@five = 5
  $six = 6
end
seven = 7

One.constants
# => [:Two]
One.instance_methods(true)
# => [:three]
One.instance_variables
# => [:@four]
One.class_variables
# => [:@@five]
global_variables.grep(/six/)
# => [:$six]
local_variables
# => [:seven]

A Symbol object differs from a String object in that a Symbol object represents an identifier, while a String object represents text or data.

What’s Here

First, what’s elsewhere. Class Symbol:

• Inherits from class Object.

• Includes module Comparable.

Here, class Symbol provides methods that are useful for:

• Querying

• Comparing

• Converting

Methods for Querying

• ::all_symbols: Returns an array of the symbols currently in Ruby’s symbol table.

• =~: Returns the index of the first substring in symbol that matches a given Regexp or other object; returns nil if no match is found.

• [], slice : Returns a substring of symbol determined by a given index, start/length, or range, or string.

• empty?: Returns true if self.length is zero; false otherwise.

• encoding: Returns the Encoding object that represents the encoding of symbol.

• end_with?: Returns true if symbol ends with any of the given strings.

• match: Returns a MatchData object if symbol matches a given Regexp; nil otherwise.

• match?: Returns true if symbol matches a given Regexp; false otherwise.

• length, size: Returns the number of characters in symbol.

• start_with?: Returns true if symbol starts with any of the given strings.

Methods for Comparing

• <=>: Returns -1, 0, or 1 as a given symbol is smaller than, equal to, or larger than symbol.

• ==, ===: Returns true if a given symbol has the same content and encoding.

• casecmp: Ignoring case, returns -1, 0, or 1 as a given symbol is smaller than, equal to, or larger than symbol.

• casecmp?: Returns true if symbol is equal to a given symbol after Unicode case folding; false otherwise.

Methods for Converting

• capitalize: Returns symbol with the first character upcased and all other characters downcased.

• downcase: Returns symbol with all characters downcased.

• inspect: Returns the string representation of self as a symbol literal.

• name: Returns the frozen string corresponding to symbol.

• succ, next: Returns the symbol that is the successor to symbol.

• swapcase: Returns symbol with all upcase characters downcased and all downcase characters upcased.

• to_proc: Returns a Proc object which responds to the method named by symbol.

• to_s, id2name: Returns the string corresponding to self.

• to_sym, intern: Returns self.

• upcase: Returns symbol with all characters upcased.

IPSocket is the super class of TCPSocket and UDPSocket.

UDPSocket represents a UDP/IP socket.

TCPServer represents a TCP/IP server socket.

A simple TCP server may look like:

require 'socket'

server = TCPServer.new 2000 # Server bind to port 2000
loop do
  client = server.accept    # Wait for a client to connect
  client.puts "Hello !"
  client.puts "Time is #{Time.now}"
  client.close
end

A more usable server (serving multiple clients):

require 'socket'

server = TCPServer.new 2000
loop do
  Thread.start(server.accept) do |client|
    client.puts "Hello !"
    client.puts "Time is #{Time.now}"
    client.close
  end
end

TCPSocket represents a TCP/IP client socket.

A simple client may look like:

require 'socket'

s = TCPSocket.new 'localhost', 2000

while line = s.gets # Read lines from socket
  puts line         # and print them
end

s.close             # close socket when done

MatchData encapsulates the result of matching a Regexp against string. It is returned by Regexp#match and String#match, and also stored in a global variable returned by Regexp.last_match.

Usage:

url = 'https://docs.ruby-lang.org/en/2.5.0/MatchData.html'
m = url.match(/(\d\.?)+/)   # => #<MatchData "2.5.0" 1:"0">
m.string                    # => "https://docs.ruby-lang.org/en/2.5.0/MatchData.html"
m.regexp                    # => /(\d\.?)+/
# entire matched substring:
m[0]                        # => "2.5.0"

# Working with unnamed captures
m = url.match(%r{([^/]+)/([^/]+)\.html$})
m.captures                  # => ["2.5.0", "MatchData"]
m[1]                        # => "2.5.0"
m.values_at(1, 2)           # => ["2.5.0", "MatchData"]

# Working with named captures
m = url.match(%r{(?<version>[^/]+)/(?<module>[^/]+)\.html$})
m.captures                  # => ["2.5.0", "MatchData"]
m.named_captures            # => {"version"=>"2.5.0", "module"=>"MatchData"}
m[:version]                 # => "2.5.0"
m.values_at(:version, :module)
                            # => ["2.5.0", "MatchData"]
# Numerical indexes are working, too
m[1]                        # => "2.5.0"
m.values_at(1, 2)           # => ["2.5.0", "MatchData"]

Global variables equivalence

Parts of last MatchData (returned by Regexp.last_match) are also aliased as global variables:

• $~ is Regexp.last_match;

• $& is Regexp.last_match[ 0 ];

• $1, $2, and so on are Regexp.last_match[ i ] (captures by number);

• $` is Regexp.last_match.pre_match;

• $' is Regexp.last_match.post_match;

• $+ is Regexp.last_match[ -1 ] (the last capture).

See also Global Variables at Regexp.

Raised in case of a stack overflow.

def me_myself_and_i
  me_myself_and_i
end
me_myself_and_i

raises the exception:

SystemStackError: stack level too deep

Load multiple documents given in yaml. Returns the parsed documents as a list.

Example:

Psych.safe_load_stream("--- foo\n...\n--- bar\n...") # => ['foo', 'bar']

list = []
Psych.safe_load_stream("--- foo\n...\n--- bar\n...") do |ruby|
  list << ruby
end
list # => ['foo', 'bar']

Load the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to false.

NOTE: This method *should not* be used to parse untrusted documents, such as YAML documents that are supplied via user input. Instead, please use the safe_load_file method.

Safely loads the document contained in filename. Returns the yaml contained in filename as a Ruby object, or if the file is empty, it returns the specified fallback return value, which defaults to nil. See safe_load for options.

Enumerator::Chain is a subclass of Enumerator, which represents a chain of enumerables that works as a single enumerator.

This type of objects can be created by Enumerable#chain and Enumerator#+.

Thrown when PTY::check is called for a pid that represents a process that has exited.

UDP/IP address information used by Socket.udp_server_loop.