Creates an accessor method to allow assignment to the attribute symbol.id2name. String arguments are converted to symbols. Returns an array of defined method names as symbols.
Checks for a constant with the given name in mod. If inherit is set, the lookup will also search the ancestors (and Object if mod is a Module).
The value of the constant is returned if a definition is found, otherwise a NameError is raised.
Math.const_get(:PI) #=> 3.14159265358979
This method will recursively look up constant names if a namespaced class name is provided. For example:
module Foo; class Bar; end end Object.const_get 'Foo::Bar'
The inherit flag is respected on each lookup. For example:
module Foo class Bar VAL = 10 end class Baz < Bar; end end Object.const_get 'Foo::Baz::VAL' # => 10 Object.const_get 'Foo::Baz::VAL', false # => NameError
If the argument is not a valid constant name a NameError will be raised with a warning “wrong constant name”.
Object.const_get 'foobar' #=> NameError: wrong constant name foobar
Sets the named constant to the given object, returning that object. Creates a new constant if no constant with the given name previously existed.
Math.const_set("HIGH_SCHOOL_PI", 22.0/7.0) #=> 3.14285714285714 Math::HIGH_SCHOOL_PI - Math::PI #=> 0.00126448926734968
If sym or str is not a valid constant name a NameError will be raised with a warning “wrong constant name”.
Object.const_set('foobar', 42) #=> NameError: wrong constant name foobar
Says whether mod or its ancestors have a constant with the given name:
Float.const_defined?(:EPSILON) #=> true, found in Float itself Float.const_defined?("String") #=> true, found in Object (ancestor) BasicObject.const_defined?(:Hash) #=> false
If mod is a Module, additionally Object and its ancestors are checked:
Math.const_defined?(:String) #=> true, found in Object
In each of the checked classes or modules, if the constant is not present but there is an autoload for it, true is returned directly without autoloading:
module Admin autoload :User, 'admin/user' end Admin.const_defined?(:User) #=> true
If the constant is not found the callback const_missing is not called and the method returns false.
If inherit is false, the lookup only checks the constants in the receiver:
IO.const_defined?(:SYNC) #=> true, found in File::Constants (ancestor) IO.const_defined?(:SYNC, false) #=> false, not found in IO itself
In this case, the same logic for autoloading applies.
If the argument is not a valid constant name a NameError is raised with the message “wrong constant name name”:
Hash.const_defined? 'foobar' #=> NameError: wrong constant name foobar
Removes the definition of the given constant, returning that constant’s previous value. If that constant referred to a module, this will not change that module’s name and can lead to confusion.
Invoked when a reference is made to an undefined constant in mod. It is passed a symbol for the undefined constant, and returns a value to be used for that constant. For example, consider:
def Foo.const_missing(name) name # return the constant name as Symbol end Foo::UNDEFINED_CONST #=> :UNDEFINED_CONST: symbol returned
As the example above shows, const_missing is not required to create the missing constant in mod, though that is often a side-effect. The caller gets its return value when triggered. If the constant is also defined, further lookups won’t hit const_missing and will return the value stored in the constant as usual. Otherwise, const_missing will be invoked again.
In the next example, when a reference is made to an undefined constant, const_missing attempts to load a file whose path is the lowercase version of the constant name (thus class Fred is assumed to be in file fred.rb). If defined as a side-effect of loading the file, the method returns the value stored in the constant. This implements an autoload feature similar to Kernel#autoload and Module#autoload, though it differs in important ways.
def Object.const_missing(name) @looked_for ||= {} str_name = name.to_s raise "Constant not found: #{name}" if @looked_for[str_name] @looked_for[str_name] = 1 file = str_name.downcase require file const_get(name, false) end
Returns an array of the names of class variables in mod. This includes the names of class variables in any included modules, unless the inherit parameter is set to false.
class One @@var1 = 1 end class Two < One @@var2 = 2 end One.class_variables #=> [:@@var1] Two.class_variables #=> [:@@var2, :@@var1] Two.class_variables(false) #=> [:@@var2]
Makes a list of existing constants public.
Makes a list of existing constants private.
Makes a list of existing constants deprecated. Attempt to refer to them will produce a warning.
module HTTP NotFound = Exception.new NOT_FOUND = NotFound # previous version of the library used this name deprecate_constant :NOT_FOUND end HTTP::NOT_FOUND # warning: constant HTTP::NOT_FOUND is deprecated
Returns true if mod is a singleton class or false if it is an ordinary class or module.
class C end C.singleton_class? #=> false C.singleton_class.singleton_class? #=> true
Return the accept character set for all new CGI instances.
Equivalent to >> with argument n.
Equivalent to << with argument n.
Equivalent to >> with argument n * 12.
Equivalent to << with argument n * 12.
Returns a hash of the name/value pairs, to use in pattern matching. Possible keys are: :year, :month, :day, :wday, :yday.
Possible usages:
d = Date.new(2022, 10, 5) if d in wday: 3, day: ..7 # uses deconstruct_keys underneath puts "first Wednesday of the month" end #=> prints "first Wednesday of the month" case d in year: ...2022 puts "too old" in month: ..9 puts "quarter 1-3" in wday: 1..5, month: puts "working day in month #{month}" end #=> prints "working day in month 10"
Note that deconstruction by pattern can also be combined with class check:
if d in Date(wday: 3, day: ..7) puts "first Wednesday of the month" end
See as_json.
Methods Date#as_json and Date.json_create may be used to serialize and deserialize a Date object; see Marshal.
Method Date#as_json serializes self, returning a 2-element hash representing self:
require 'json/add/date' x = Date.today.as_json # => {"json_class"=>"Date", "y"=>2023, "m"=>11, "d"=>21, "sg"=>2299161.0}
Method JSON.create deserializes such a hash, returning a Date object:
Date.json_create(x) # => #<Date: 2023-11-21 ((2460270j,0s,0n),+0s,2299161j)>
Returns a JSON string representing self:
require 'json/add/date' puts Date.today.to_json
Output:
{"json_class":"Date","y":2023,"m":11,"d":21,"sg":2299161.0}
Returns a hash of the name/value pairs, to use in pattern matching. Possible keys are: :year, :month, :day, :wday, :yday, :hour, :min, :sec, :sec_fraction, :zone.
Possible usages:
dt = DateTime.new(2022, 10, 5, 13, 30) if d in wday: 1..5, hour: 10..18 # uses deconstruct_keys underneath puts "Working time" end #=> prints "Working time" case dt in year: ...2022 puts "too old" in month: ..9 puts "quarter 1-3" in wday: 1..5, month: puts "working day in month #{month}" end #=> prints "working day in month 10"
Note that deconstruction by pattern can also be combined with class check:
if d in DateTime(wday: 1..5, hour: 10..18, day: ..7) puts "Working time, first week of the month" end
Methods DateTime#as_json and DateTime.json_create may be used to serialize and deserialize a DateTime object; see Marshal.
Method DateTime#as_json serializes self, returning a 2-element hash representing self:
require 'json/add/datetime' x = DateTime.now.as_json # => {"json_class"=>"DateTime", "y"=>2023, "m"=>11, "d"=>21, "sg"=>2299161.0}
Method JSON.create deserializes such a hash, returning a DateTime object:
DateTime.json_create(x) # BUG? Raises Date::Error "invalid date"
Returns a JSON string representing self:
require 'json/add/datetime' puts DateTime.now.to_json
Output:
{"json_class":"DateTime","y":2023,"m":11,"d":21,"sg":2299161.0}