abstract struct Struct

Overview

Struct is the base type of structs you create in your program. It is set as a struct's superstruct when you don't specify one:

struct Foo # < Struct
end

Structs inherit from Value so they are allocated on the stack and passed by value. For this reason you should prefer using structs for immutable data types and/or stateless wrappers of other types.

Mutable structs are still allowed, but code involving them must remember that passing a struct to a method actually passes a copy to it, so the method should return the modified struct:

struct Mutable
  property value

  def initialize(@value : Int32)
  end
end

def change_bad(mutable)
  mutable.value = 2
end

def change_good(mutable)
  mutable.value = 2
  mutable
end

mut = Mutable.new 1
change_bad(mut)
mut.value # => 1

mut = change_good(mut)
mut.value # => 2

The standard library provides a useful record macro that allows you to create immutable structs with some fields, similar to a Tuple but using names instead of indices.

Direct Known Subclasses

Defined in:

struct.cr

Instance Method Summary

#==(other) : Bool
Returns true if this struct is equal to other.
#hash(hasher)
See Object#hash(hasher)
#inspect(io : IO) : Nil
Appends this struct's name and instance variables names and values to the given IO.
#pretty_print(pp) : Nil
#to_s(io : IO) : Nil
Same as #inspect(io).

Instance methods inherited from struct `Value`

Instance methods inherited from class `Object`

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Class methods inherited from class `Object`

Instance Method Detail

def ==(other) : Bool Source

Returns true if this struct is equal to other.

Both structs' instance vars are compared to each other. Thus, two structs are considered equal if each of their instance variables are equal. Subclasses should override this method to provide specific equality semantics.

struct Point
  def initialize(@x : Int32, @y : Int32)
  end
end

p1 = Point.new 1, 2
p2 = Point.new 1, 2
p3 = Point.new 3, 4

p1 == p2 # => true
p1 == p3 # => false

def hash(hasher)Source

See Object#hash(hasher)

def inspect(io : IO) : Nil Source

Appends this struct's name and instance variables names and values to the given IO.

struct Point
  def initialize(@x : Int32, @y : Int32)
  end
end

p1 = Point.new 1, 2
p1.to_s    # "Point(@x=1, @y=2)"
p1.inspect # "Point(@x=1, @y=2)"

def pretty_print(pp) : Nil Source

def to_s(io : IO) : Nil Source

Same as #inspect(io).

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Licensed under the Apache License, Version 2.0.
https://crystal-lang.org/api/1.2.1/Struct.html

abstract struct Struct

Overview

Direct Known Subclasses

Defined in:

Instance Method Summary

Instance methods inherited from struct Value

Instance methods inherited from class Object

Class methods inherited from class Object

Instance Method Detail

def ==(other) : BoolSource