ruby_and_iterators

Ruby

Control Flow, Functions, and Iterators

Control flow

Javascript (Some Control Flow Structures)

• Conditionals
  • if, else if, else, ...
• Loops
  • while, for, for...in, ...
• Iterators,
  • .forEach, .map, .filter, ...

Ruby (Some Control Flow Structures)

• Conditionals
  • if, elsif, else, unless, ...
• Loops
  • until, while, times ...
• iterators,
  • .each, .map, .select, ...

Examples

If/Else

course = "wdi"
if course == "uxdi"
    puts "Hello, User Experience Designer!"
elsif course == "fewd"
    puts "Hello, Front-End Developer"
elsif course == "wdi"
    puts "Hello, Immersed Student"
else
    puts "Who are you?"
end

Loops

i = 0
while i < 5 do
   puts "i is " + i.to_s
   i += 1
end

... is the same as ...

i = 0
until i == 5 do
   puts "i is " + i.to_s
   i += 1
end

... is the same as ...

5.times do |i|
   puts "i is #{i}"
end

# Will _all_ print out:
# >i is 0
# >i is 1
# >i is 2
# >i is 3
# >i is 4

Iterating through Arrays

foods = ["carrots", "kale", "beets"]
foods.each do |vegetable|
    puts "i like #{vegetable}"
end

... is the same as ...

for veg in ["carrots", "kale", "beets"] do
    puts "i like #{veg}"
end

# Will _each_ print out:
# >i like carrots
# >i like kale
# >i like beets

Iterating through Hashes

car = {wheels: 4,doors: 2,seats: 5}
car.each do |key, num|
  puts "my car has #{num} #{key}"
end

# Will print out:
# my car has 4 wheels
# my car has 2 doors
# my car has 5 seats

Functions

Javascript

• Function
  • anonymous: function (param1, [..param2, [...]]){...},
  • named: function Name(param1, [..param2, [...]]){...}
  • uses lexical scope
  • used as values
  • require explicit return
  • all params are optional

Ruby

• Function
  • uses def
  • does not capture scope
  • not used as values
  • optional parameters must be specified
  • implicitly returns last evaluation

Examples

Convert several examples of JavaScript functions into the equivalent Ruby.

Syntax

JavaScript:

var sayHello = function () {
    console.log("Hello, World!");
};

sayHello();

Ruby:

def say_hello
    puts "Hello, World!"
end

say_hello()

... is the same as ...

def say_hello
    puts "Hello, World!"
end

# note missing parentheses
say_hello

In Ruby, leaving the () off of a function call is acceptable. Since functions can't be passed as values (i.e., aren't first-class), Ruby knows that we mean to call the function, so it calls it.

Parameters (Arguments)

JavaScript:

var sayHello = function (friend) {
    console.log("Hello, " + friend + "!");
};
sayHello("Tim");

Ruby:

def say_hello(friend)
    puts "Hello, #{friend}!"
end
say_hello("Tim")

... is the same as ...

def say_hello(friend)
    puts "Hello, #{friend}!"
end
# note the lack of parentheses
say_hello "Tim"

Return Values

JavaScript:

var add = function (num1, num2) {
    return num1 + num2;
};
var sum = add(2, 3);
console.log("2 + 3 = " + sum);

Ruby:

def add(num1, num2)
    return num1 + num2
end
sum = add(2, 3)
puts "2 + 3 = #{sum}"

... is the same as ...

def add(num1, num2)
    # note the lack of explicit return
    num1 + num2
end
sum = add(2, 3)
puts "2 + 3 = #{sum}"

Ruby will automatically return the value of the last evaluated expression. This is called having "implicit returns". You are free to have an explicit return statement, but you don't have to.

... and finally ...

def add num1, num2
    num1 + num2
end
sum = add 2, 3
puts "2 + 3 = #{sum}"

Iterators

Ruby has many / all of the iterator methods you've grown to love. Sometimes they even have fun new names.

Map (i.e., Collect)

[1,2,3].map do |num|
    num * 5
end

[1,2,3].collect do |num|
    num * 5
end

# both return [5,10,15]

Filter (i.e., Select)

[1,2,3].select do |num|
    num % 2 == 0
end
# returns [2]

Reduce (i.e., Inject)

[1,2,3].reduce do |totalSoFar, num|
    totalSoFar + num
end
# returns 6

["tim", "bob", "frank"].inject do |jumbledMess, name|
    jumbledMess.concat(name)
end
# returns "timbobfrank"