Results for: "OptionParser"

Encoding::Converter

Encoding conversion class.

CGI::QueryExtension

Mixin module that provides the following:

  1. Access to the CGI environment variables as methods. See documentation to the CGI class for a list of these variables. The methods are exposed by removing the leading HTTP_ (if it exists) and downcasing the name. For example, auth_type will return the environment variable AUTH_TYPE, and accept will return the value for HTTP_ACCEPT.

  2. Access to cookies, including the cookies attribute.

  3. Access to parameters, including the params attribute, and overloading [] to perform parameter value lookup by key.

  4. The initialize_query method, for initializing the above mechanisms, handling multipart forms, and allowing the class to be used in “offline” mode.

DidYouMean::NameErrorCheckers

No documentation available

Gem::GemcutterUtilities

Utility methods for using the RubyGems API.

Gem::InstallerUninstallerUtils

Helper methods for both Gem::Installer and Gem::Uninstaller

Array

An Array is an ordered, integer-indexed collection of objects, called elements. Any object may be an Array element.

Array Indexes

Array indexing starts at 0, as in C or Java.

A positive index is an offset from the first element:

A negative index is an offset, backwards, from the end of the array:

A non-negative index is in range if it is smaller than the size of the array. For a 3-element array:

A negative index is in range if its absolute value is not larger than the size of the array. For a 3-element array:

Creating Arrays

You can create an Array object explicitly with:

You can convert certain objects to Arrays with:

An Array can contain different types of objects. For example, the array below contains an Integer, a String and a Float:

ary = [1, "two", 3.0] #=> [1, "two", 3.0]

An array can also be created by calling Array.new with zero, one (the initial size of the Array) or two arguments (the initial size and a default object).

ary = Array.new    #=> []
Array.new(3)       #=> [nil, nil, nil]
Array.new(3, true) #=> [true, true, true]

Note that the second argument populates the array with references to the same object. Therefore, it is only recommended in cases when you need to instantiate arrays with natively immutable objects such as Symbols, numbers, true or false.

To create an array with separate objects a block can be passed instead. This method is safe to use with mutable objects such as hashes, strings or other arrays:

Array.new(4) {Hash.new}    #=> [{}, {}, {}, {}]
Array.new(4) {|i| i.to_s } #=> ["0", "1", "2", "3"]

This is also a quick way to build up multi-dimensional arrays:

empty_table = Array.new(3) {Array.new(3)}
#=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]

An array can also be created by using the Array() method, provided by Kernel, which tries to call to_ary, then to_a on its argument.

Array({:a => "a", :b => "b"}) #=> [[:a, "a"], [:b, "b"]]

Example Usage

In addition to the methods it mixes in through the Enumerable module, the Array class has proprietary methods for accessing, searching and otherwise manipulating arrays.

Some of the more common ones are illustrated below.

Accessing Elements

Elements in an array can be retrieved using the Array#[] method. It can take a single integer argument (a numeric index), a pair of arguments (start and length) or a range. Negative indices start counting from the end, with -1 being the last element.

arr = [1, 2, 3, 4, 5, 6]
arr[2]    #=> 3
arr[100]  #=> nil
arr[-3]   #=> 4
arr[2, 3] #=> [3, 4, 5]
arr[1..4] #=> [2, 3, 4, 5]
arr[1..-3] #=> [2, 3, 4]

Another way to access a particular array element is by using the at method

arr.at(0) #=> 1

The slice method works in an identical manner to Array#[].

To raise an error for indices outside of the array bounds or else to provide a default value when that happens, you can use fetch.

arr = ['a', 'b', 'c', 'd', 'e', 'f']
arr.fetch(100) #=> IndexError: index 100 outside of array bounds: -6...6
arr.fetch(100, "oops") #=> "oops"

The special methods first and last will return the first and last elements of an array, respectively.

arr.first #=> 1
arr.last  #=> 6

To return the first n elements of an array, use take

arr.take(3) #=> [1, 2, 3]

drop does the opposite of take, by returning the elements after n elements have been dropped:

arr.drop(3) #=> [4, 5, 6]

Obtaining Information about an Array

Arrays keep track of their own length at all times. To query an array about the number of elements it contains, use length, count or size.

browsers = ['Chrome', 'Firefox', 'Safari', 'Opera', 'IE']
browsers.length #=> 5
browsers.count #=> 5

To check whether an array contains any elements at all

browsers.empty? #=> false

To check whether a particular item is included in the array

browsers.include?('Konqueror') #=> false

Adding Items to Arrays

Items can be added to the end of an array by using either push or <<

arr = [1, 2, 3, 4]
arr.push(5) #=> [1, 2, 3, 4, 5]
arr << 6    #=> [1, 2, 3, 4, 5, 6]

unshift will add a new item to the beginning of an array.

arr.unshift(0) #=> [0, 1, 2, 3, 4, 5, 6]

With insert you can add a new element to an array at any position.

arr.insert(3, 'apple')  #=> [0, 1, 2, 'apple', 3, 4, 5, 6]

Using the insert method, you can also insert multiple values at once:

arr.insert(3, 'orange', 'pear', 'grapefruit')
#=> [0, 1, 2, "orange", "pear", "grapefruit", "apple", 3, 4, 5, 6]

Removing Items from an Array

The method pop removes the last element in an array and returns it:

arr =  [1, 2, 3, 4, 5, 6]
arr.pop #=> 6
arr #=> [1, 2, 3, 4, 5]

To retrieve and at the same time remove the first item, use shift:

arr.shift #=> 1
arr #=> [2, 3, 4, 5]

To delete an element at a particular index:

arr.delete_at(2) #=> 4
arr #=> [2, 3, 5]

To delete a particular element anywhere in an array, use delete:

arr = [1, 2, 2, 3]
arr.delete(2) #=> 2
arr #=> [1,3]

A useful method if you need to remove nil values from an array is compact:

arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact! #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, 'bar', 7, 'baz']

Another common need is to remove duplicate elements from an array.

It has the non-destructive uniq, and destructive method uniq!

arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]

Iterating over Arrays

Like all classes that include the Enumerable module, Array has an each method, which defines what elements should be iterated over and how. In case of Array’s each, all elements in the Array instance are yielded to the supplied block in sequence.

Note that this operation leaves the array unchanged.

arr = [1, 2, 3, 4, 5]
arr.each {|a| print a -= 10, " "}
# prints: -9 -8 -7 -6 -5
#=> [1, 2, 3, 4, 5]

Another sometimes useful iterator is reverse_each which will iterate over the elements in the array in reverse order.

words = %w[first second third fourth fifth sixth]
str = ""
words.reverse_each {|word| str += "#{word} "}
p str #=> "sixth fifth fourth third second first "

The map method can be used to create a new array based on the original array, but with the values modified by the supplied block:

arr.map {|a| 2*a}     #=> [2, 4, 6, 8, 10]
arr                   #=> [1, 2, 3, 4, 5]
arr.map! {|a| a**2}   #=> [1, 4, 9, 16, 25]
arr                   #=> [1, 4, 9, 16, 25]

Selecting Items from an Array

Elements can be selected from an array according to criteria defined in a block. The selection can happen in a destructive or a non-destructive manner. While the destructive operations will modify the array they were called on, the non-destructive methods usually return a new array with the selected elements, but leave the original array unchanged.

Non-destructive Selection 

arr = [1, 2, 3, 4, 5, 6]
arr.select {|a| a > 3}       #=> [4, 5, 6]
arr.reject {|a| a < 3}       #=> [3, 4, 5, 6]
arr.drop_while {|a| a < 4}   #=> [4, 5, 6]
arr                          #=> [1, 2, 3, 4, 5, 6]

Destructive Selection

select! and reject! are the corresponding destructive methods to select and reject

Similar to select vs. reject, delete_if and keep_if have the exact opposite result when supplied with the same block:

arr.delete_if {|a| a < 4}   #=> [4, 5, 6]
arr                         #=> [4, 5, 6]

arr = [1, 2, 3, 4, 5, 6]
arr.keep_if {|a| a < 4}   #=> [1, 2, 3]
arr                       #=> [1, 2, 3]

What’s Here

First, what’s elsewhere. Class Array:

Here, class Array provides methods that are useful for:

Methods for Creating an Array

::[]

Returns a new array populated with given objects.

::new

Returns a new array.

::try_convert

Returns a new array created from a given object.

Methods for Querying

length, size

Returns the count of elements.

include?

Returns whether any element == a given object.

empty?

Returns whether there are no elements.

all?

Returns whether all elements meet a given criterion.

any?

Returns whether any element meets a given criterion.

none?

Returns whether no element == a given object.

one?

Returns whether exactly one element == a given object.

count

Returns the count of elements that meet a given criterion.

find_index, index

Returns the index of the first element that meets a given criterion.

rindex

Returns the index of the last element that meets a given criterion.

hash

Returns the integer hash code.

Methods for Comparing

#<=>

Returns -1, 0, or 1 as self is less than, equal to, or greater than a given object.

#==

Returns whether each element in self is == to the corresponding element in a given object.

eql?

Returns whether each element in self is eql? to the corresponding element in a given object.

Methods for Fetching

These methods do not modify self.

[]

Returns one or more elements.

fetch

Returns the element at a given offset.

first

Returns one or more leading elements.

last

Returns one or more trailing elements.

max

Returns one or more maximum-valued elements, as determined by <=> or a given block.

max

Returns one or more minimum-valued elements, as determined by <=> or a given block.

minmax

Returns the minimum-valued and maximum-valued elements, as determined by <=> or a given block.

assoc

Returns the first element that is an array whose first element == a given object.

rassoc

Returns the first element that is an array whose second element == a given object.

at

Returns the element at a given offset.

values_at

Returns the elements at given offsets.

dig

Returns the object in nested objects that is specified by a given index and additional arguments.

drop

Returns trailing elements as determined by a given index.

take

Returns leading elements as determined by a given index.

drop_while

Returns trailing elements as determined by a given block.

take_while

Returns leading elements as determined by a given block.

slice

Returns consecutive elements as determined by a given argument.

sort

Returns all elements in an order determined by <=> or a given block.

reverse

Returns all elements in reverse order.

compact

Returns an array containing all non-nil elements.

select, filter

Returns an array containing elements selected by a given block.

uniq

Returns an array containing non-duplicate elements.

rotate

Returns all elements with some rotated from one end to the other.

bsearch

Returns an element selected via a binary search as determined by a given block.

bsearch_index

Returns the index of an element selected via a binary search as determined by a given block.

sample

Returns one or more random elements.

shuffle

Returns elements in a random order.

Methods for Assigning

These methods add, replace, or reorder elements in self.

[]=

Assigns specified elements with a given object.

push, append, <<

Appends trailing elements.

unshift, prepend

Prepends leading elements.

insert

Inserts given objects at a given offset; does not replace elements.

concat

Appends all elements from given arrays.

fill

Replaces specified elements with specified objects.

replace

Replaces the content of self with the content of a given array.

reverse!

Replaces self with its elements reversed.

rotate!

Replaces self with its elements rotated.

shuffle!

Replaces self with its elements in random order.

sort!

Replaces self with its elements sorted, as determined by <=> or a given block.

sort_by!

Replaces self with its elements sorted, as determined by a given block.

Methods for Deleting

Each of these methods removes elements from self:

pop

Removes and returns the last element.

shift

Removes and returns the first element.

compact!

Removes all non-nil elements.

delete

Removes elements equal to a given object.

delete_at

Removes the element at a given offset.

delete_if

Removes elements specified by a given block.

keep_if

Removes elements not specified by a given block.

reject!

Removes elements specified by a given block.

select!, filter!

Removes elements not specified by a given block.

slice!

Removes and returns a sequence of elements.

uniq!

Removes duplicates.

Methods for Combining

#&

Returns an array containing elements found both in self and a given array.

intersection

Returns an array containing elements found both in self and in each given array.

+

Returns an array containing all elements of self followed by all elements of a given array.

-

Returns an array containiing all elements of self that are not found in a given array.

#|

Returns an array containing all elements of self and all elements of a given array, duplicates removed.

union

Returns an array containing all elements of self and all elements of given arrays, duplicates removed.

difference

Returns an array containing all elements of self that are not found in any of the given arrays..

product

Returns or yields all combinations of elements from self and given arrays.

Methods for Iterating

each

Passes each element to a given block.

reverse_each

Passes each element, in reverse order, to a given block.

each_index

Passes each element index to a given block.

cycle

Calls a given block with each element, then does so again, for a specified number of times, or forever.

combination

Calls a given block with combinations of elements of self; a combination does not use the same element more than once.

permutation

Calls a given block with permutations of elements of self; a permutation does not use the same element more than once.

repeated_combination

Calls a given block with combinations of elements of self; a combination may use the same element more than once.

repeated_permutation

Calls a given block with permutations of elements of self; a permutation may use the same element more than once.

Methods for Converting

map, collect

Returns an array containing the block return-value for each element.

map!, collect!

Replaces each element with a block return-value.

flatten

Returns an array that is a recursive flattening of self.

flatten!

Replaces each nested array in self with the elements from that array.

inspect, to_s

Returns a new String containing the elements.

join

Returns a newsString containing the elements joined by the field separator.

to_a

Returns self or a new array containing all elements.

to_ary

Returns self.

to_h

Returns a new hash formed from the elements.

transpose

Transposes self, which must be an array of arrays.

zip

Returns a new array of arrays containing self and given arrays; follow the link for details.

Other Methods

*

Returns one of the following:

  • With integer argument n, a new array that is the concatenation of n copies of self.

  • With string argument field_separator, a new string that is equivalent to join(field_separator).

abbrev

Returns a hash of unambiguous abbreviations for elements.

pack

Packs the elements into a binary sequence.

sum

Returns a sum of elements according to either + or a given block.

for pack.c

Integer

An Integer object represents an integer value.

You can create an Integer object explicitly with:

You can convert certain objects to Integers with:

An attempt to add a singleton method to an instance of this class causes an exception to be raised.

What’s Here

First, what’s elsewhere. Class Integer:

Here, class Integer provides methods for:

Querying

Comparing

Converting

Other

Numeric

Numeric is the class from which all higher-level numeric classes should inherit.

Numeric allows instantiation of heap-allocated objects. Other core numeric classes such as Integer are implemented as immediates, which means that each Integer is a single immutable object which is always passed by value.

a = 1
1.object_id == a.object_id   #=> true

There can only ever be one instance of the integer 1, for example. Ruby ensures this by preventing instantiation. If duplication is attempted, the same instance is returned.

Integer.new(1)                   #=> NoMethodError: undefined method `new' for Integer:Class
1.dup                            #=> 1
1.object_id == 1.dup.object_id   #=> true

For this reason, Numeric should be used when defining other numeric classes.

Classes which inherit from Numeric must implement coerce, which returns a two-member Array containing an object that has been coerced into an instance of the new class and self (see coerce).

Inheriting classes should also implement arithmetic operator methods (+, -, * and /) and the <=> operator (see Comparable). These methods may rely on coerce to ensure interoperability with instances of other numeric classes.

class Tally < Numeric
  def initialize(string)
    @string = string
  end

  def to_s
    @string
  end

  def to_i
    @string.size
  end

  def coerce(other)
    [self.class.new('|' * other.to_i), self]
  end

  def <=>(other)
    to_i <=> other.to_i
  end

  def +(other)
    self.class.new('|' * (to_i + other.to_i))
  end

  def -(other)
    self.class.new('|' * (to_i - other.to_i))
  end

  def *(other)
    self.class.new('|' * (to_i * other.to_i))
  end

  def /(other)
    self.class.new('|' * (to_i / other.to_i))
  end
end

tally = Tally.new('||')
puts tally * 2            #=> "||||"
puts tally > 1            #=> true

What’s Here

First, what’s elsewhere. Class Numeric:

Here, class Numeric provides methods for:

Querying

Comparing

Converting

Other

Fiber

Fibers are primitives for implementing light weight cooperative concurrency in Ruby. Basically they are a means of creating code blocks that can be paused and resumed, much like threads. The main difference is that they are never preempted and that the scheduling must be done by the programmer and not the VM.

As opposed to other stackless light weight concurrency models, each fiber comes with a stack. This enables the fiber to be paused from deeply nested function calls within the fiber block. See the ruby(1) manpage to configure the size of the fiber stack(s).

When a fiber is created it will not run automatically. Rather it must be explicitly asked to run using the Fiber#resume method. The code running inside the fiber can give up control by calling Fiber.yield in which case it yields control back to caller (the caller of the Fiber#resume).

Upon yielding or termination the Fiber returns the value of the last executed expression

For instance:

fiber = Fiber.new do
  Fiber.yield 1
  2
end

puts fiber.resume
puts fiber.resume
puts fiber.resume

produces

1
2
FiberError: dead fiber called

The Fiber#resume method accepts an arbitrary number of parameters, if it is the first call to resume then they will be passed as block arguments. Otherwise they will be the return value of the call to Fiber.yield

Example:

fiber = Fiber.new do |first|
  second = Fiber.yield first + 2
end

puts fiber.resume 10
puts fiber.resume 1_000_000
puts fiber.resume "The fiber will be dead before I can cause trouble"

produces

12
1000000
FiberError: dead fiber called

Non-blocking Fibers

The concept of non-blocking fiber was introduced in Ruby 3.0. A non-blocking fiber, when reaching a operation that would normally block the fiber (like sleep, or wait for another process or I/O) will yield control to other fibers and allow the scheduler to handle blocking and waking up (resuming) this fiber when it can proceed.

For a Fiber to behave as non-blocking, it need to be created in Fiber.new with blocking: false (which is the default), and Fiber.scheduler should be set with Fiber.set_scheduler. If Fiber.scheduler is not set in the current thread, blocking and non-blocking fibers’ behavior is identical.

Ruby doesn’t provide a scheduler class: it is expected to be implemented by the user and correspond to Fiber::SchedulerInterface.

There is also Fiber.schedule method, which is expected to immediately perform the given block in a non-blocking manner. Its actual implementation is up to the scheduler.

Enumerator

A class which allows both internal and external iteration.

An Enumerator can be created by the following methods.

Most methods have two forms: a block form where the contents are evaluated for each item in the enumeration, and a non-block form which returns a new Enumerator wrapping the iteration.

enumerator = %w(one two three).each
puts enumerator.class # => Enumerator

enumerator.each_with_object("foo") do |item, obj|
  puts "#{obj}: #{item}"
end

# foo: one
# foo: two
# foo: three

enum_with_obj = enumerator.each_with_object("foo")
puts enum_with_obj.class # => Enumerator

enum_with_obj.each do |item, obj|
  puts "#{obj}: #{item}"
end

# foo: one
# foo: two
# foo: three

This allows you to chain Enumerators together. For example, you can map a list’s elements to strings containing the index and the element as a string via:

puts %w[foo bar baz].map.with_index { |w, i| "#{i}:#{w}" }
# => ["0:foo", "1:bar", "2:baz"]

An Enumerator can also be used as an external iterator. For example, Enumerator#next returns the next value of the iterator or raises StopIteration if the Enumerator is at the end.

e = [1,2,3].each   # returns an enumerator object.
puts e.next   # => 1
puts e.next   # => 2
puts e.next   # => 3
puts e.next   # raises StopIteration

Note that enumeration sequence by next, next_values, peek and peek_values do not affect other non-external enumeration methods, unless the underlying iteration method itself has side-effect, e.g. IO#each_line.

Moreover, implementation typically uses fibers so performance could be slower and exception stacktraces different than expected.

You can use this to implement an internal iterator as follows:

def ext_each(e)
  while true
    begin
      vs = e.next_values
    rescue StopIteration
      return $!.result
    end
    y = yield(*vs)
    e.feed y
  end
end

o = Object.new

def o.each
  puts yield
  puts yield(1)
  puts yield(1, 2)
  3
end

# use o.each as an internal iterator directly.
puts o.each {|*x| puts x; [:b, *x] }
# => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

# convert o.each to an external iterator for
# implementing an internal iterator.
puts ext_each(o.to_enum) {|*x| puts x; [:b, *x] }
# => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

TypeError

Raised when encountering an object that is not of the expected type.

[1, 2, 3].first("two")

raises the exception:

TypeError: no implicit conversion of String into Integer

IndexError

Raised when the given index is invalid.

a = [:foo, :bar]
a.fetch(0)   #=> :foo
a[4]         #=> nil
a.fetch(4)   #=> IndexError: index 4 outside of array bounds: -2...2

KeyError

Raised when the specified key is not found. It is a subclass of IndexError.

h = {"foo" => :bar}
h.fetch("foo") #=> :bar
h.fetch("baz") #=> KeyError: key not found: "baz"

RangeError

Raised when a given numerical value is out of range.

[1, 2, 3].drop(1 << 100)

raises the exception:

RangeError: bignum too big to convert into `long'

SyntaxError

Raised when encountering Ruby code with an invalid syntax.

eval("1+1=2")

raises the exception:

SyntaxError: (eval):1: syntax error, unexpected '=', expecting $end

LoadError

Raised when a file required (a Ruby script, extension library, …) fails to load.

require 'this/file/does/not/exist'

raises the exception:

LoadError: no such file to load -- this/file/does/not/exist

NameError

Raised when a given name is invalid or undefined.

puts foo

raises the exception:

NameError: undefined local variable or method `foo' for main:Object

Since constant names must start with a capital:

Integer.const_set :answer, 42

raises the exception:

NameError: wrong constant name answer

NoMethodError

Raised when a method is called on a receiver which doesn’t have it defined and also fails to respond with method_missing.

"hello".to_ary

raises the exception:

NoMethodError: undefined method `to_ary' for "hello":String

FrozenError

Raised when there is an attempt to modify a frozen object.

[1, 2, 3].freeze << 4

raises the exception:

FrozenError: can't modify frozen Array

NoMemoryError

Raised when memory allocation fails.

EncodingError

EncodingError is the base class for encoding errors.

SystemCallError

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

DateTime

DateTime

A subclass of Date that easily handles date, hour, minute, second, and offset.

DateTime class is considered deprecated. Use Time class.

DateTime does not consider any leap seconds, does not track any summer time rules.

A DateTime object is created with DateTime::new, DateTime::jd, DateTime::ordinal, DateTime::commercial, DateTime::parse, DateTime::strptime, DateTime::now, Time#to_datetime, etc.

require 'date'

DateTime.new(2001,2,3,4,5,6)
                    #=> #<DateTime: 2001-02-03T04:05:06+00:00 ...>

The last element of day, hour, minute, or second can be a fractional number. The fractional number’s precision is assumed at most nanosecond.

DateTime.new(2001,2,3.5)
                    #=> #<DateTime: 2001-02-03T12:00:00+00:00 ...>

An optional argument, the offset, indicates the difference between the local time and UTC. For example, Rational(3,24) represents ahead of 3 hours of UTC, Rational(-5,24) represents behind of 5 hours of UTC. The offset should be -1 to +1, and its precision is assumed at most second. The default value is zero (equals to UTC).

DateTime.new(2001,2,3,4,5,6,Rational(3,24))
                    #=> #<DateTime: 2001-02-03T04:05:06+03:00 ...>

The offset also accepts string form:

DateTime.new(2001,2,3,4,5,6,'+03:00')
                    #=> #<DateTime: 2001-02-03T04:05:06+03:00 ...>

An optional argument, the day of calendar reform (start), denotes a Julian day number, which should be 2298874 to 2426355 or negative/positive infinity. The default value is Date::ITALY (2299161=1582-10-15).

A DateTime object has various methods. See each reference.

d = DateTime.parse('3rd Feb 2001 04:05:06+03:30')
                    #=> #<DateTime: 2001-02-03T04:05:06+03:30 ...>
d.hour              #=> 4
d.min               #=> 5
d.sec               #=> 6
d.offset            #=> (7/48)
d.zone              #=> "+03:30"
d += Rational('1.5')
                    #=> #<DateTime: 2001-02-04%16:05:06+03:30 ...>
d = d.new_offset('+09:00')
                    #=> #<DateTime: 2001-02-04%21:35:06+09:00 ...>
d.strftime('%I:%M:%S %p')
                    #=> "09:35:06 PM"
d > DateTime.new(1999)
                    #=> true

When should you use DateTime and when should you use Time?

It’s a common misconception that William Shakespeare and Miguel de Cervantes died on the same day in history - so much so that UNESCO named April 23 as World Book Day because of this fact. However, because England hadn’t yet adopted the Gregorian Calendar Reform (and wouldn’t until 1752) their deaths are actually 10 days apart. Since Ruby’s Time class implements a proleptic Gregorian calendar and has no concept of calendar reform there’s no way to express this with Time objects. This is where DateTime steps in:

shakespeare = DateTime.iso8601('1616-04-23', Date::ENGLAND)
 #=> Tue, 23 Apr 1616 00:00:00 +0000
cervantes = DateTime.iso8601('1616-04-23', Date::ITALY)
 #=> Sat, 23 Apr 1616 00:00:00 +0000

Already you can see something is weird - the days of the week are different. Taking this further:

cervantes == shakespeare
 #=> false
(shakespeare - cervantes).to_i
 #=> 10

This shows that in fact they died 10 days apart (in reality 11 days since Cervantes died a day earlier but was buried on the 23rd). We can see the actual date of Shakespeare’s death by using the gregorian method to convert it:

shakespeare.gregorian
 #=> Tue, 03 May 1616 00:00:00 +0000

So there’s an argument that all the celebrations that take place on the 23rd April in Stratford-upon-Avon are actually the wrong date since England is now using the Gregorian calendar. You can see why when we transition across the reform date boundary:

# start off with the anniversary of Shakespeare's birth in 1751
shakespeare = DateTime.iso8601('1751-04-23', Date::ENGLAND)
 #=> Tue, 23 Apr 1751 00:00:00 +0000

# add 366 days since 1752 is a leap year and April 23 is after February 29
shakespeare + 366
 #=> Thu, 23 Apr 1752 00:00:00 +0000

# add another 365 days to take us to the anniversary in 1753
shakespeare + 366 + 365
 #=> Fri, 04 May 1753 00:00:00 +0000

As you can see, if we’re accurately tracking the number of solar years since Shakespeare’s birthday then the correct anniversary date would be the 4th May and not the 23rd April.

So when should you use DateTime in Ruby and when should you use Time? Almost certainly you’ll want to use Time since your app is probably dealing with current dates and times. However, if you need to deal with dates and times in a historical context you’ll want to use DateTime to avoid making the same mistakes as UNESCO. If you also have to deal with timezones then best of luck - just bear in mind that you’ll probably be dealing with local solar times, since it wasn’t until the 19th century that the introduction of the railways necessitated the need for Standard Time and eventually timezones.

Time

Time is an abstraction of dates and times. Time is stored internally as the number of seconds with subsecond since the Epoch, 1970-01-01 00:00:00 UTC.

The Time class treats GMT (Greenwich Mean Time) and UTC (Coordinated Universal Time) as equivalent. GMT is the older way of referring to these baseline times but persists in the names of calls on POSIX systems.

Note: A Time object uses the resolution available on your system clock.

All times may have subsecond. Be aware of this fact when comparing times with each other – times that are apparently equal when displayed may be different when compared. (Since Ruby 2.7.0, Time#inspect shows subsecond but Time#to_s still doesn’t show subsecond.)

Examples

All of these examples were done using the EST timezone which is GMT-5.

Creating a New Time Instance

You can create a new instance of Time with Time.new. This will use the current system time. Time.now is an alias for this. You can also pass parts of the time to Time.new such as year, month, minute, etc. When you want to construct a time this way you must pass at least a year. If you pass the year with nothing else time will default to January 1 of that year at 00:00:00 with the current system timezone. Here are some examples:

Time.new(2002)         #=> 2002-01-01 00:00:00 -0500
Time.new(2002, 10)     #=> 2002-10-01 00:00:00 -0500
Time.new(2002, 10, 31) #=> 2002-10-31 00:00:00 -0500

You can pass a UTC offset:

Time.new(2002, 10, 31, 2, 2, 2, "+02:00") #=> 2002-10-31 02:02:02 +0200

Or a timezone object:

zone = timezone("Europe/Athens")      # Eastern European Time, UTC+2
Time.new(2002, 10, 31, 2, 2, 2, zone) #=> 2002-10-31 02:02:02 +0200

You can also use Time.local and Time.utc to infer local and UTC timezones instead of using the current system setting.

You can also create a new time using Time.at which takes the number of seconds (with subsecond) since the Unix Epoch.

Time.at(628232400) #=> 1989-11-28 00:00:00 -0500

Working with an Instance of Time

Once you have an instance of Time there is a multitude of things you can do with it. Below are some examples. For all of the following examples, we will work on the assumption that you have done the following:

t = Time.new(1993, 02, 24, 12, 0, 0, "+09:00")

Was that a monday?

t.monday? #=> false

What year was that again?

t.year #=> 1993

Was it daylight savings at the time?

t.dst? #=> false

What’s the day a year later?

t + (60*60*24*365) #=> 1994-02-24 12:00:00 +0900

How many seconds was that since the Unix Epoch?

t.to_i #=> 730522800

You can also do standard functions like compare two times.

t1 = Time.new(2010)
t2 = Time.new(2011)

t1 == t2 #=> false
t1 == t1 #=> true
t1 <  t2 #=> true
t1 >  t2 #=> false

Time.new(2010,10,31).between?(t1, t2) #=> true

What’s Here

First, what’s elsewhere. Class Time:

Here, class Time provides methods that are useful for:

Methods for Creating

Methods for Fetching

Methods for Querying

Methods for Comparing

Methods for Converting

Methods for Rounding

Timezone Argument

A timezone argument must have local_to_utc and utc_to_local methods, and may have name, abbr, and dst? methods.

The local_to_utc method should convert a Time-like object from the timezone to UTC, and utc_to_local is the opposite. The result also should be a Time or Time-like object (not necessary to be the same class). The zone of the result is just ignored. Time-like argument to these methods is similar to a Time object in UTC without subsecond; it has attribute readers for the parts, e.g. year, month, and so on, and epoch time readers, to_i. The subsecond attributes are fixed as 0, and utc_offset, zone, isdst, and their aliases are same as a Time object in UTC. Also to_time, +, and - methods are defined.

The name method is used for marshaling. If this method is not defined on a timezone object, Time objects using that timezone object can not be dumped by Marshal.

The abbr method is used by ‘%Z’ in strftime.

The dst? method is called with a Time value and should return whether the Time value is in daylight savings time in the zone.

Auto Conversion to Timezone

At loading marshaled data, a timezone name will be converted to a timezone object by find_timezone class method, if the method is defined.

Similarly, that class method will be called when a timezone argument does not have the necessary methods mentioned above.

IO

Expect library adds the IO instance method expect, which does similar act to tcl’s expect extension.

In order to use this method, you must require expect:

require 'expect'

Please see expect for usage.

The IO class is the basis for all input and output in Ruby. An I/O stream may be duplexed (that is, bidirectional), and so may use more than one native operating system stream.

Many of the examples in this section use the File class, the only standard subclass of IO. The two classes are closely associated. Like the File class, the Socket library subclasses from IO (such as TCPSocket or UDPSocket).

The Kernel#open method can create an IO (or File) object for these types of arguments:

The IO may be opened with different file modes (read-only, write-only) and encodings for proper conversion. See IO.new for these options. See Kernel#open for details of the various command formats described above.

IO.popen, the Open3 library, or Process#spawn may also be used to communicate with subprocesses through an IO.

Ruby will convert pathnames between different operating system conventions if possible. For instance, on a Windows system the filename "/gumby/ruby/test.rb" will be opened as "\gumby\ruby\test.rb". When specifying a Windows-style filename in a Ruby string, remember to escape the backslashes:

"C:\\gumby\\ruby\\test.rb"

Our examples here will use the Unix-style forward slashes; File::ALT_SEPARATOR can be used to get the platform-specific separator character.

The global constant ARGF (also accessible as $<) provides an IO-like stream which allows access to all files mentioned on the command line (or STDIN if no files are mentioned). ARGF#path and its alias ARGF#filename are provided to access the name of the file currently being read.

io/console

The io/console extension provides methods for interacting with the console. The console can be accessed from IO.console or the standard input/output/error IO objects.

Requiring io/console adds the following methods:

Example:

require 'io/console'
rows, columns = $stdout.winsize
puts "Your screen is #{columns} wide and #{rows} tall"

Example Files

Many examples here use these filenames and their corresponding files:

Modes

A number of IO method calls must or may specify a mode for the stream; the mode determines how stream is to be accessible, including:

Mode Specified as an Integer

When mode is an integer it must be one or more (combined by bitwise OR (|) of the modes defined in File::Constants:

Examples:

File.new('t.txt', File::RDONLY)
File.new('t.tmp', File::RDWR | File::CREAT | File::EXCL)

Note: Method IO#set_encoding does not allow the mode to be specified as an integer.

Mode Specified As a String

When mode is a string it must begin with one of the following:

For a writable file stream (that is, any except read-only), the file is truncated to zero if it exists, and is created if it does not exist.

Examples:

File.open('t.txt', 'r')
File.open('t.tmp', 'w')

Either of the following may be suffixed to any of the above:

If neither is given, the stream defaults to text data.

Examples:

File.open('t.txt', 'rt')
File.open('t.dat', 'rb')

The following may be suffixed to any writable mode above:

Example:

File.open('t.tmp', 'wx')

Finally, the mode string may specify encodings – either external encoding only or both external and internal encodings – by appending one or both encoding names, separated by colons:

f = File.new('t.dat', 'rb')
f.external_encoding # => #<Encoding:ASCII-8BIT>
f.internal_encoding # => nil
f = File.new('t.dat', 'rb:UTF-16')
f.external_encoding # => #<Encoding:UTF-16 (dummy)>
f.internal_encoding # => nil
f = File.new('t.dat', 'rb:UTF-16:UTF-16')
f.external_encoding # => #<Encoding:UTF-16 (dummy)>
f.internal_encoding # => #<Encoding:UTF-16>

The numerous encoding names are available in array Encoding.name_list:

Encoding.name_list.size    # => 175
Encoding.name_list.take(3) # => ["ASCII-8BIT", "UTF-8", "US-ASCII"]

Encodings

When the external encoding is set, strings read are tagged by that encoding when reading, and strings written are converted to that encoding when writing.

When both external and internal encodings are set, strings read are converted from external to internal encoding, and strings written are converted from internal to external encoding. For further details about transcoding input and output, see Encoding.

If the external encoding is 'BOM|UTF-8', 'BOM|UTF-16LE' or 'BOM|UTF16-BE', Ruby checks for a Unicode BOM in the input document to help determine the encoding. For UTF-16 encodings the file open mode must be binary. If the BOM is found, it is stripped and the external encoding from the BOM is used.

Note that the BOM-style encoding option is case insensitive, so ‘bom|utf-8’ is also valid.)

Open Options

A number of IO methods accept an optional parameter opts, which determines how a new stream is to be opened:

Also available are the options offered in String#encode, which may control conversion between external internal encoding.

Getline Options

A number of IO methods accept optional keyword arguments that determine how a stream is to be treated:

Position

An IO stream has a position, which is the non-negative integer offset (in bytes) in the stream where the next read or write will occur.

Note that a text stream may have multi-byte characters, so a text stream whose position is n (bytes) may not have n characters preceding the current position – there may be fewer.

A new stream is initially positioned:

Methods to query the position:

Reading from a stream usually changes its position:

f = File.open('t.txt')
f.tell     # => 0
f.readline # => "This is line one.\n"
f.tell     # => 19
f.readline # => "This is the second line.\n"
f.tell     # => 45
f.eof?     # => false
f.readline # => "Here's the third line.\n"
f.eof?     # => true

Writing to a stream usually changes its position:

f = File.open('t.tmp', 'w')
f.tell         # => 0
f.write('foo') # => 3
f.tell         # => 3
f.write('bar') # => 3
f.tell         # => 6

Iterating over a stream usually changes its position:

f = File.open('t.txt')
f.each do |line|
  p "position=#{f.pos} eof?=#{f.eof?} line=#{line}"
end

Output:

"position=19 eof?=false line=This is line one.\n"
"position=45 eof?=false line=This is the second line.\n"
"position=70 eof?=true line=This is the third line.\n"

The position may also be changed by certain other methods:

Line Number

A readable IO stream has a line number, which is the non-negative integer line number in the stream where the next read will occur.

A new stream is initially has line number 0.

Method IO#lineno returns the line number.

Reading lines from a stream usually changes its line number:

f = File.open('t.txt', 'r')
f.lineno   # => 0
f.readline # => "This is line one.\n"
f.lineno   # => 1
f.readline # => "This is the second line.\n"
f.lineno   # => 2
f.readline # => "Here's the third line.\n"
f.lineno   # => 3
f.eof?     # => true

Iterating over lines in a stream usually changes its line number:

f = File.open('t.txt')
f.each_line do |line|
  p "position=#{f.pos} eof?=#{f.eof?} line=#{line}"
end

Output:

"position=19 eof?=false line=This is line one.\n"
"position=45 eof?=false line=This is the second line.\n"
"position=70 eof?=true line=This is the third line.\n"

What’s Here

First, what’s elsewhere. Class IO:

Here, class IO provides methods that are useful for:

Creating

Reading

Writing

Positioning

Iterating

Settings

Querying

Buffering

Low-Level Access

Other

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