Learn Crystal in One Video
Crystal is one of the most exciting new languages to come out in some time, so I decided to teach the core language in one video. Crystal is as easy to use as Ruby, but has the speed of C. In this one video I’ll cover Data Types, Strings, Arrays, Map, Looping, Conditionals, Math, Hashes, Tuples, Procs, Functions, Enums, Symbols, Classes, Inheritance, Modules, Polymorphism, Structs, Exceptions, File IO and More.
A cheat follows the video below to help you learn.
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Cheat Sheet
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# Crystal utilizes code that is as easy # to understand as Ruby, but has the speed # of C # Output to the console puts "Hello World" # ----- DATA TYPES ----- # Everything is an object # Variables start with _ or a lowercase # letter and may contain numbers # This is a constant PI = 3.14 # You can assign multiple values a, b = 1, 2 # Bools are either true or false canIVote = true # sizeof returns the size in bytes puts sizeof(Int8) puts sizeof(Int16) puts sizeof(Int32) puts sizeof(Int64) # There are also unsigned versions # UInt8, UInt16, UInt32, UInt64 # There are 2 float types Float32 & Float64 # They are accurate up to around 13 digits bigFloat = 1.12345678901234 # You can cast to a string using .to_s puts (bigFloat + 0.00000000000005).to_s # A Char is surrounded by single quotes # and is either a single character or # a special character like \n, \t, \', \" myGrade = 'A' # ----- STRINGS ----- # Strings are a series of characters # surrounded by "" myName = "Derek" num1 = 1 num2 = 2 # String interpolation is available puts "#{num1} + #{num2} = #{num1 + num2}" # Multiline strings multString = "I use many lines" puts multString # Concatenate strings puts myName + " Banas" # String size puts "Egg".size # Duplicate string puts "Money " * 3 # Compare equality puts "Doug" == "Paul" # Returns -1, 0, or 1 puts "Doug".compare("Paul") # Get value at index puts "Hello"[0] # Index where value is puts "Monkey".index("key") # Does string contain a string puts "Turtledove".includes?("dove") # Get a range of values puts "Pigman"[0..2] # Return an array of Chars puts "Sue".chars # Return an array using a separator puts "Happy Birthday".split(" ") # Number of times a character is used puts "Derek".count('e') # Check if empty puts "".empty? # Replace substring with another puts "Have a good day".gsub("good") {"ok"} # Insert in a string puts "Have a day".insert(6, " good") # ----- ARRAYS ----- # Arrays are ordered lists with integer indexes # Create array array1 = [8,4,3,7,9] # You can use multiple types array2 = [5, "Word", 3.2] # You can define accepted types array3 = [1,2,3] of String | Int32 # Empty arrays should specify a type array4 = Array(Int32).new # Assign values to array using a separator names = "Paul,Sue,Sam".split(",") # Get size puts array1.size # Get index puts array1[1] # Get from index to other puts array1[1, 4] # Get last puts array1[-1] # Add value array1 << 10 # Remove last value puts array1.pop # Remove 1st puts array1.shift # Check if value exists puts array1.includes? 7 # Delete values array1.delete(7) # Delete from index to index puts array1.delete_at(0,2) # Insert a value at index and shift values puts array1.insert(0, 3) # Push on multiple values puts array1.push(4,5,6,7) # Sort values puts array1.sort # Return uniques puts array1.uniq # Perform operation on all values puts array1.map! {|x| x * x} # Return array of all permutations puts array1.permutations # Output array in loop array1.each do |value| puts value end # ----- LOOPING ----- # Print evens from 1 to 10 x = 1 loop do x += 1 # Skip rest of loop unless even next unless (x % 2) == 0 puts x # Stop looping if x >= 10 break if x >= 10 end # While loops as long as a condition is true y = 1 while y <= 10 y += 1 next unless (y % 2) == 0 puts y break if y >= 10 end # Loop until a condition is met a = 1 until a >= 10 a += 1 next unless (a % 2) == 0 puts a end # ----- CONDITIONALS ----- # Comparison Operators : == != < > <= >= # Logical Operators : && || ! (and, or, not) age = 12 if (age >= 5) && (age <= 6) puts "You're in Kindergarten" elsif (age >= 7) && (age <= 13) puts "You're in Middle School" puts "Yeah" elsif (age >= 14) && (age <= 18) puts "You're in High School" else puts "Stay Home" end puts "true || false = " + (true || false).to_s puts "!true = " + (!true).to_s # Unless comparison unless age > 4 puts "No School" else puts "Go to School" end # Case is used with limited options print "Language : " lang = gets case lang when "French", "french" puts "Bonjour" # without end it would check the next condition exit when "Spanish", "spanish" puts "Hola" exit # else is the default else puts "Hello" end # Ternary operator age = 55 puts (age >= 50) ? "Old" : "Young" # ----- USER INTERACTION & MATH ----- print "Enter 1st value " # Get input from the user # not_nil! provides us with a way to handle # nil inputs which I cover later with # exception handling n1 = gets.not_nil! print "Enter 2nd value " n2 = gets.not_nil! # to_i converts a string into an int # to_s, to_f, to_f64, to_i64, etc. puts "#{n1} + #{n2} = #{n1.to_i + n2.to_i}" puts "#{n1} - #{n2} = #{n1.to_i - n2.to_i}" puts "#{n1} * #{n2} = #{n1.to_i * n2.to_i}" puts "#{n1} / #{n2} = #{n1.to_i / n2.to_i}" puts "#{n1} % #{n2} = #{n1.to_i % n2.to_i}" puts "#{n1} ** #{n2} = #{n1.to_i ** n2.to_i}" # Trig functions cos, sin, tan, acos, asin, # atan, cosh, sinh, tanh, acosh, asinh, atanh puts "sqrt(#{n1}) = #{Math.cbrt(n1.to_i)}" puts "cbrt(#{n1}) = #{Math.cbrt(n1.to_i)}" puts "hypot(2,2) = #{Math.hypot(2,2)}" puts "log(100) = #{Math.log(100)}" puts "log10(100) = #{Math.log10(100)}" puts "log2(100) = #{Math.log2(100)}" puts "max(100,101) = #{Math.max(100,101)}" puts "min(100,101) = #{Math.min(100,101)}" # ----- HASHES ----- # A hash is a collection of key object pairs nHash = { "PI" => 3.14, "Golden" => 1.618, "e" => 2.718} puts nHash["PI"] # Print out each key and value nHash.each do |key, value| puts key.to_s + " : " + value.to_s end puts "Size of Hash : " + nHash.size.to_s # Check if empty puts nHash.empty? # Check for key nHash.has_key?("PI") # Check for value nHash.has_value?(3.14) # Merge hashes nHash.merge({"Absolute0" => -459}) # Get hash without keys puts nHash.reject("PI") # Return based on value condition puts nHash.select {|k, v| v > 2} # Remove all but given keys puts nHash.select!("PI") # Delete using key nHash.delete("PI") # Delete if condition is true nHash.delete_if {|key, value| key.starts_with?("Go")} # Clear a hash nHash.clear # ----- TUPLES ----- # Tuples are fixed in size, may have different types # Create a tuple t1 = {"Derek", 43, 174.5} # Value at index puts t1[0] # Loop through tuple t1.each do |value| puts value end # Get first value or use last? puts t1.first? # Get size puts t1.size # ----- PROCS ----- # Procs represent a function pointer proc = ->(x : Int32) {x * x} puts proc.call 5 # ----- FUNCTIONS ----- # Functions start with def, name, # parameters if any and maybe a return # value def addNums(n1, n2) return n1 + n2 end puts addNums(5,4) # Variables are pass by value x = 1 def changeX(x) x = 5 end puts x # A function can receive a variable # number of arguments using a splat def getSum(*vals) sum = 0 vals.each do |val| sum += val end vals end puts getSum 1,2,3,4 # ----- ENUMS ----- # Enums have a collection of names # associated with an int starting with 0 # You can assign a datatype or use Int32 enum Color : UInt8 Blue Red Green = 4 # You can change a value # You can have methods def green? # Check if enum is assigned to green self == Color::Green end end # Get the value puts Color::Green.value # Check if enum is green puts Color::Green.green? # ----- SYMBOLS ----- # Symbols are strings that can't change # We'll cover them later with classes :Derek puts :Derek # ----- CLASSES ----- # Classes are blueprints used to model # real world objects # Object attributes are called fields # Object capabilities are called methods class Animal # Called when an Animal object is created def initialize(name : String) puts "Animal created" @name = name end def setName(name) # Set value for the field @name = name end def getName # Return name value @name end # Another way to get the name value def name @name end # Protect our name data def name=(name) if name.is_a?(Number) puts "Name can't be a number" else @name = name end end end # Create an Animal cat = Animal.new("Mittens") # Change name cat.name = 1 cat.name = "Sophie" # Get name of cat puts cat.getName class Dog # Shortcut for creating getters and setters property name : String property height : Float32 property weight : Float32 def initialize @name = "No name" @height = 0 @weight = 0 end def bark return "Bark" end end rover = Dog.new rover.name = "Rover" puts "#{rover.name} says #{rover.bark}" # Inherit all fields and methods of Dog class GermanShephard < Dog def bark return "Loud Bark" end end max = GermanShephard.new max.name = "Max" puts "#{max.name} says #{max.bark}" # ----- MODULES ----- # Modules add functionality to a class # but they can't be instantiated module Vehicle def makeSound puts "Rumm Rummmmm" end end class MacTruck include Vehicle end macTruck = MacTruck.new macTruck.makeSound # ----- POLYMORPHISM ----- # Crystal uses duck typing to achieve # polymorphism class Bird def tweet(bird_type) bird_type.tweet end end class Cardinal < Bird def tweet puts "Tweet tweet" end end class Parrot < Bird def tweet puts "Squawk" end end generic_bird = Bird.new generic_bird.tweet(Cardinal.new) generic_bird.tweet(Parrot.new) # ----- STRUCTS ----- # Structs allow you to create light weight # classes with some built in functionality struct Location property lat : Float32 property long : Float32 def initialize(@lat : Float32, @long : Float32) end def position puts "Latitude : #{lat} Longitude : #{long}" end end where = Location.new(80.31, 72.62) where.position # ----- EXCEPTION HANDLING ----- # We catch exceptions with begin and rescue print "Enter a number : " fNum = gets.not_nil! print "Enter Another : " sNum = gets.not_nil! begin answer = fNum.to_i / sNum.to_i rescue # You could use rescue ZeroDivisionError puts "You can't divide by zero" exit end puts "#{fNum} / #{sNum} = #{answer}" # You can throw your own exceptions with raise # You catch them with rescue age = -1 begin if(age < 0) raise "Enter Positive Number" end rescue ex puts "That is an impossible age" end # ----- FILE IO ----- # Returns a File object for writing write_handler = File.new("somefile.out", "w") # Puts the text in the file write_handler.puts("Random Text").to_s # Closes the file write_handler.close # Read data from the defined file data_from_file = File.read("somefile.out") puts "Data From File : " + data_from_file |
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