ktanaka101

Int32.new("+1") #=> 1
Int32.new("-1") #=> -1

"+1".to_i #=> 1
"-1".to_i #=> -1

ktanaka101

type_id = 0b0001 
flags = [false, true, false, true]

(type_id & 0x0F) << 4
((type_id & 0x0F) << 4).to_u8 |
      (flags[3] ? 0x8_u8 : 0x0_u8) |
      (flags[2] ? 0x4_u8 : 0x0_u8) |
      (flags[1] ? 0x2_u8 : 0x0_u8) |
      (flags[0] ? 0x1_u8 : 0x0_u8)

ktanaka101

0xFFFFFFFF
0b11111111111111111111111111111111

0xFF_FF_FF_FF
0b11111111_11111111_11111111_11111111

ktanaka101

# crystal

enum Abc : UInt8
  A = 0x00
  B = 0x01
  C = 0x02
end

Abc::A + 2 #=> C : Abc

ktanaka101

module MyInterface
end

class MyClass
  include MyInterface
end

MyClass.new.is_a?(MyClass) #=> true
MyClass.new.is_a?(MyInterface) #=> true
[MyClass.new].is_a?(Array(MyClass)) #=> true

ktanaka101

class MyProtocol
  module MyInterface
  end

  def initialize(@clients : Array(MyInterface))
  end
end

class MyClient
  include MyProtocol::MyInterface

ktanaka101

# crystal
module Interface
  def a
  end
end

class Cls1
  include Interface
end

ktanaka101

# crystal

class ABC
end

def ABC.new
  false
end

ABC.new #=> false

ktanaka101

# crystal
a = [1, 2, 3]
b = [1, 2, 3]
a == b  #=> true
a === b #=> true

a = {1, 2, 3}
b = {1, 2, 3}
a == b  #=> true
a === b #=> true

ktanaka101

# crystal
{"a" => 1, "b" => 2} #=> {"a" => 1, "b" => 2} : Hash(String, Int32)
a = {"a": 1, "b": 2} #=> {a: 1, b: 2} : NamedTuple(a: Int32, b: Int32)

{"a" => 1, "b": 2} #=> {"a" => 1, "b" => 2}
{"a": 1, "b" => 2} #=> Syntax error in :6: space not allowed between named argument name and ':'