Deserializes the given JSON in string_or_io into an instance of self, assuming the JSON consists of an JSON object with key root, and whose value is the value to deserialize.

Int32.from_json(%({"main": 1}), root: "main") # => 1

Deserializes the given JSON in string_or_io into an instance of self. This simply creates a parser = JSON::PullParser and invokes new(parser): classes that want to provide JSON deserialization must provide an def initialize(parser : JSON::PullParser) method.

Int32.from_json("1")                # => 1
Array(Int32).from_json("[1, 2, 3]") # => [1, 2, 3]

Returns true if this object is not equal to other.

By default this method is implemented as !(self == other) so there's no need to override this unless there's a more efficient way to do it.

Shortcut to !(self =~ other).

Returns true if this object is equal to other.

Subclasses override this method to provide class-specific meaning.

Case equality.

The #=== method is used in a case ... when ... end expression.

For example, this code:

case value
when x
  # something when x
when y
  # something when y
end

Is equivalent to this code:

if x === value
  # something when x
elsif y === value
  # something when y
end

Object simply implements #=== by invoking #==, but subclasses (notably Regex) can override it to provide meaningful case-equality semantics.

Pattern match.

Overridden by descendants (notably Regex and String) to provide meaningful pattern-match semantics.

Returns the runtime Class of an object.

1.class       # => Int32
"hello".class # => String

Compare it with typeof, which returns the compile-time type of an object:

random_value = rand # => 0.627423
value = random_value < 0.5 ? 1 : "hello"
value         # => "hello"
value.class   # => String
typeof(value) # => Int32 | String

Returns a shallow copy of this object.

As a convention, clone is the method used to create a deep copy of an object, but this logic isn't defined generically for every type because cycles could be involved, and the clone logic might not need to clone everything.

Many types in the standard library, like Array, Hash, Set and Deque, and all primitive types, define #dup and clone.

Generates an Int hash value for this object.

This method must have the property that a == b implies a.hash == b.hash.

The hash value is used along with #== by the Hash class to determine if two objects reference the same hash key.

Appends a string representation of this object to the given IO object.

Similar to #to_s(io), but usually appends more information about this object.

Returns a String representation of this object.

Similar to #to_s, but usually returns more information about this object.

Classes must usually not override this method. Instead, they must override #inspect(io), which must append to the given IO object.

Return self.

str = "hello"
str.itself.object_id == str.object_id # => true

Returns self. Nil overrides this method and raises an exception.

Returns a pretty printed version of self.

Pretty prints self into the given printer.

By default appends a text that is the result of invoking #inspect on self. Subclasses should override for custom pretty printing.

Yields self to the block, and then returns self.

The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.

(1..10).tap { |x| puts "original: #{x.inspect}" }
       .to_a.tap { |x| puts "array: #{x.inspect}" }
            .select { |x| x % 2 == 0 }.tap { |x| puts "evens: #{x.inspect}" }
                                      .map { |x| x*x }.tap { |x| puts "squares: #{x.inspect}" }

Returns a string representation of this object.

Descendants must usually not override this method. Instead, they must override #to_s(io), which must append to the given IO object.

Appends a String representation of this object to the given IO object.

An object must never append itself to the io argument, as this will in turn call #to_s(io) on it.

Yields self. Nil overrides this method and doesn't yield.

This method is useful for dealing with nilable types, to safely perform operations only when the value is not nil.

# First program argument in downcase, or nil
ARGV[0]?.try &.downcase

Unsafely reinterprets the bytes of an object as being of another type.

This method is useful to treat a type that is represented as a chunk of bytes as another type where those bytes convey useful information. As an example, you can check the individual bytes of an Int32:

0x01020304.unsafe_as(StaticArray(UInt8, 4)) # => StaticArray[4, 3, 2, 1]

Or treat the bytes of a Float64 as an Int64:

1.234_f64.unsafe_as(Int64) # => 4608236261112822104

This method is unsafe because it behaves unpredictably when the given type doesn't have the same bytesize as the receiver, or when the given type representation doesn't semantically match the underlying bytes.

Also note that because #unsafe_as is a regular method, unlike the pseudo-method as, you can't specify some types in the type grammar using a short notation, so specifying a static array must always be done as StaticArray(T, N), a tuple as Tuple(...) and so on, never as UInt8[4] or {Int32, Int32}.

Defines getter methods for each of the given arguments.

Writing:

class Person
  class_getter name
end

Is the same as writing:

class Person
  def self.name
    @@name
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_getter :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  class_getter name : String
end

Is the same as writing:

class Person
  @@name : String

  def self.name : String
    @@name
  end
end

The type declaration can also include an initial value:

class Person
  class_getter name : String = "John Doe"
end

Is the same as writing:

class Person
  @@name : String = "John Doe"

  def self.name : String
    @@name
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  class_getter name = "John Doe"
end

Is the same as writing:

class Person
  @@name = "John Doe"

  def self.name : String
    @@name
  end
end

If a block is given to the macro, a getter is generated with a variable that is lazily initialized with the block's contents:

class Person
  class_getter(birth_date) { Time.now }
end

Is the same as writing:

class Person
  def self.birth_date
    @@birth_date ||= Time.now
  end
end

Defines raise-on-nil and nilable getter methods for each of the given arguments.

Writing:

class Person
  class_getter! name
end

Is the same as writing:

class Person
  def self.name?
    @@name
  end

  def self.name
    @@name.not_nil!
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_getter! :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type, as nilable.

class Person
  class_getter! name : String
end

is the same as writing:

class Person
  @@name : String?

  def self.name?
    @@name
  end

  def self.name
    @@name.not_nil!
  end
end

Defines query getter methods for each of the given arguments.

Writing:

class Person
  class_getter? happy
end

Is the same as writing:

class Person
  def self.happy?
    @@happy
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_getter? :happy, "famous"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  class_getter? happy : Bool
end

is the same as writing:

class Person
  @@happy : Bool

  def self.happy? : Bool
    @@happy
  end
end

The type declaration can also include an initial value:

class Person
  class_getter? happy : Bool = true
end

Is the same as writing:

class Person
  @@happy : Bool = true

  def self.happy? : Bool
    @@happy
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  class_getter? happy = true
end

Is the same as writing:

class Person
  @@happy = true

  def self.happy?
    @@happy
  end
end

Defines property methods for each of the given arguments.

Writing:

class Person
  class_property name
end

Is the same as writing:

class Person
  def self.name=(@@name)
  end

  def self.name
    @@name
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_property :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  class_property name : String
end

Is the same as writing:

class Person
  @@name : String

  def self.name=(@@name)
  end

  def self.name
    @@name
  end
end

The type declaration can also include an initial value:

class Person
  class_property name : String = "John Doe"
end

Is the same as writing:

class Person
  @@name : String = "John Doe"

  def self.name=(@@name : String)
  end

  def self.name
    @@name
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  class_property name = "John Doe"
end

Is the same as writing:

class Person
  @@name = "John Doe"

  def self.name=(@@name : String)
  end

  def self.name
    @@name
  end
end

If a block is given to the macro, a property is generated with a variable that is lazily initialized with the block's contents:

class Person
  class_property(birth_date) { Time.now }
end

Is the same as writing:

class Person
  def self.birth_date
    @@birth_date ||= Time.now
  end

  def self.birth_date=(@@birth_date)
  end
end

Defines raise-on-nil property methods for each of the given arguments.

Writing:

class Person
  class_property! name
end

Is the same as writing:

class Person
  def self.name=(@@name)
  end

  def self.name?
    @@name
  end

  def self.name
    @@name.not_nil!
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_property! :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type, as nilable.

class Person
  class_property! name : String
end

Is the same as writing:

class Person
  @@name : String?

  def self.name=(@@name)
  end

  def self.name?
    @@name
  end

  def self.name
    @@name.not_nil!
  end
end

Defines query property methods for each of the given arguments.

Writing:

class Person
  class_property? happy
end

Is the same as writing:

class Person
  def self.happy=(@@happy)
  end

  def self.happy?
    @@happy
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_property? :happy, "famous"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  class_property? happy : Bool
end

Is the same as writing:

class Person
  @@happy : Bool

  def self.happy=(@@happy)
  end

  def self.happy?
    @@happy
  end

  def self.happy
    @@happy.not_nil!
  end
end

The type declaration can also include an initial value:

class Person
  class_property? happy : Bool = true
end

Is the same as writing:

class Person
  @@happy : Bool = true

  def self.happy=(@@happy : Bool)
  end

  def self.happy? : Bool
    @@happy
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  class_property? happy = true
end

Is the same as writing:

class Person
  @@happy = true

  def self.happy=(@@happy)
  end

  def self.happy?
    @@happy
  end
end

Defines setter methods for each of the given arguments.

Writing:

class Person
  class_setter name
end

Is the same as writing:

class Person
  def self.name=(@@name)
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  class_setter :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  class_setter name : String
end

is the same as writing:

class Person
  @@name : String

  def self.name=(@@name : String)
  end
end

The type declaration can also include an initial value:

class Person
  class_setter name : String = "John Doe"
end

Is the same as writing:

class Person
  @@name : String = "John Doe"

  def self.name=(@@name : String)
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  class_setter name = "John Doe"
end

Is the same as writing:

class Person
  @@name = "John Doe"

  def self.name=(@@name)
  end
end

Defines a clone method that returns a copy of this object with all instance variables cloned (clone is in turn invoked on them).

Defines an #== method by comparing the given fields.

The generated #== method has a self restriction.

class Person
  def initialize(@name, @age)
  end

  # Define a `==` method that compares @name and @age
  def_equals @name, @age
end

Defines #hash and #== method from the given fields.

The generated #== method has a self restriction.

class Person
  def initialize(@name, @age)
  end

  # Define a hash method based on @name and @age
  # Define a `==` method that compares @name and @age
  def_equals_and_hash @name, @age
end

Defines a #hash method computed from the given fields.

class Person
  def initialize(@name, @age)
  end

  # Define a hash method based on @name and @age
  def_hash @name, @age
end

Delegate methods to to.

Note that due to current language limitations this is only useful when no captured blocks are involved.

class StringWrapper
  def initialize(@string : String)
  end

  delegate downcase, to: @string
  delegate gsub, to: @string
  delegate empty?, capitalize, to: @string
end

wrapper = StringWrapper.new "HELLO"
wrapper.downcase       # => "hello"
wrapper.gsub(/E/, "A") # => "HALLO"
wrapper.empty?         # => false
wrapper.capitalize     # => "Hello"

Forwards missing methods to delegate.

class StringWrapper
  def initialize(@string : String)
  end

  forward_missing_to @string
end

wrapper = StringWrapper.new "HELLO"
wrapper.downcase       # => "hello"
wrapper.gsub(/E/, "A") # => "HALLO"

Defines getter methods for each of the given arguments.

Writing:

class Person
  getter name
end

Is the same as writing:

class Person
  def name
    @name
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  getter :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  getter name : String
end

Is the same as writing:

class Person
  @name : String

  def name : String
    @name
  end
end

The type declaration can also include an initial value:

class Person
  getter name : String = "John Doe"
end

Is the same as writing:

class Person
  @name : String = "John Doe"

  def name : String
    @name
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  getter name = "John Doe"
end

Is the same as writing:

class Person
  @name = "John Doe"

  def name : String
    @name
  end
end

If a block is given to the macro, a getter is generated with a variable that is lazily initialized with the block's contents:

class Person
  getter(birth_date) { Time.now }
end

Is the same as writing:

class Person
  def birth_date
    @birth_date ||= Time.now
  end
end

Defines raise-on-nil and nilable getter methods for each of the given arguments.

Writing:

class Person
  getter! name
end

Is the same as writing:

class Person
  def name?
    @name
  end

  def name
    @name.not_nil!
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  getter! :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type, as nilable.

class Person
  getter! name : String
end

is the same as writing:

class Person
  @name : String?

  def name?
    @name
  end

  def name
    @name.not_nil!
  end
end

Defines query getter methods for each of the given arguments.

Writing:

class Person
  getter? happy
end

Is the same as writing:

class Person
  def happy?
    @happy
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  getter? :happy, "famous"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  getter? happy : Bool
end

is the same as writing:

class Person
  @happy : Bool

  def happy? : Bool
    @happy
  end
end

The type declaration can also include an initial value:

class Person
  getter? happy : Bool = true
end

Is the same as writing:

class Person
  @happy : Bool = true

  def happy? : Bool
    @happy
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  getter? happy = true
end

Is the same as writing:

class Person
  @happy = true

  def happy?
    @happy
  end
end

Defines property methods for each of the given arguments.

Writing:

class Person
  property name
end

Is the same as writing:

class Person
  def name=(@name)
  end

  def name
    @name
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  property :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  property name : String
end

Is the same as writing:

class Person
  @name : String

  def name=(@name)
  end

  def name
    @name
  end
end

The type declaration can also include an initial value:

class Person
  property name : String = "John Doe"
end

Is the same as writing:

class Person
  @name : String = "John Doe"

  def name=(@name : String)
  end

  def name
    @name
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  property name = "John Doe"
end

Is the same as writing:

class Person
  @name = "John Doe"

  def name=(@name : String)
  end

  def name
    @name
  end
end

If a block is given to the macro, a property is generated with a variable that is lazily initialized with the block's contents:

class Person
  property(birth_date) { Time.now }
end

Is the same as writing:

class Person
  def birth_date
    @birth_date ||= Time.now
  end

  def birth_date=(@birth_date)
  end
end

Defines raise-on-nil property methods for each of the given arguments.

Writing:

class Person
  property! name
end

Is the same as writing:

class Person
  def name=(@name)
  end

  def name?
    @name
  end

  def name
    @name.not_nil!
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  property! :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type, as nilable.

class Person
  property! name : String
end

Is the same as writing:

class Person
  @name : String?

  def name=(@name)
  end

  def name?
    @name
  end

  def name
    @name.not_nil!
  end
end

Defines query property methods for each of the given arguments.

Writing:

class Person
  property? happy
end

Is the same as writing:

class Person
  def happy=(@happy)
  end

  def happy?
    @happy
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  property? :happy, "famous"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  property? happy : Bool
end

Is the same as writing:

class Person
  @happy : Bool

  def happy=(@happy)
  end

  def happy?
    @happy
  end

  def happy
    @happy.not_nil!
  end
end

The type declaration can also include an initial value:

class Person
  property? happy : Bool = true
end

Is the same as writing:

class Person
  @happy : Bool = true

  def happy=(@happy : Bool)
  end

  def happy? : Bool
    @happy
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  property? happy = true
end

Is the same as writing:

class Person
  @happy = true

  def happy=(@happy)
  end

  def happy?
    @happy
  end
end

Defines setter methods for each of the given arguments.

Writing:

class Person
  setter name
end

Is the same as writing:

class Person
  def name=(@name)
  end
end

The arguments can be string literals, symbol literals or plain names:

class Person
  setter :name, "age"
end

If a type declaration is given, a variable with that name is declared with that type.

class Person
  setter name : String
end

is the same as writing:

class Person
  @name : String

  def name=(@name : String)
  end
end

The type declaration can also include an initial value:

class Person
  setter name : String = "John Doe"
end

Is the same as writing:

class Person
  @name : String = "John Doe"

  def name=(@name : String)
  end
end

An assignment can be passed too, but in this case the type of the variable must be easily inferrable from the initial value:

class Person
  setter name = "John Doe"
end

Is the same as writing:

class Person
  @name = "John Doe"

  def name=(@name)
  end
end