Snake

• Why Snake?
• It's Snake!
• Easy, but requires:
• Arrays
• Loops
• UI
• Input

Ruby

• "Scripting" language
• Dynamic types
• Used for proper stuff (e.g. GitHub)
• Looks a bit like Python (at first)
• You can often miss out . and (
• Code blocks are first-class
• Rails, Rails, Rails

Functions

• Brackets are often optional
• return is optional
• Finish block with end

def sum x, y
    x + y
end

Classes

class Game
    attr_accessor :grid_size

    def initialize grid_size
        @grid_size = grid_size
    #...
end

• Accessors are like properties in Python, Java etc.
• initialize is the constructor
• @name means instance variable

Classes

• Create with ClassName.new

game = Game.new

# Equivalently:
game = Game.new()

Flow control

if v == Up or v == Down
    game.change_dir v
elsif v == Esc
    Gtk.main_quit
else
    puts v
end

Flow control

if is_apple pos then return false end

Flow control

for x in 1..3
    puts x
end

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Blocks

• This is why Ruby is great
• Inspiration from Lisp
• Beautiful syntax

Blocks

5.times { @snake_body.push( last ) }

Blocks

w.connect( "key_press" ) do |widget, event|
    v = event.keyval
    # ...
end

• In blocks, {...} is mostly the same as do...end

Sugar

• .. is inclusive
• ... is exclusive

Sugar

for x in 1...3
    puts x
end

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Sugar

• "Splat" operator:

size = [ 3, 4 ]

@cr.rectangle 0, 0, *size

# (rectangle takes 4 arguments)

Sugar

• Looping/iteration

@game.snake_body.each do |pos|
    gfx.dot Snake_color, pos
end

Sugar

• Not switch, case:

case @snake_dir
when Up
    x = pos[0]
    y = pos[1] - 1
    # No fallthrough!
when Down
    x = pos[0]
    y = pos[1] + 1
end

Wrinkles

• newline ends a statement, if it does
• If the syntax allows a statement end
• All other whitespace is insignificant
• This is like JavaScript!

return a   # is not the same as:
return
    a

• ; always ends a statement

Wrinkles

• do starts a block, if it does
• After for and similar, it doesn't
• This affects variable scope
• Operators are really methods
• Leading capital means it's a constant

Other features

• :name is a symbol
• Operator overloading
• Everything is an expression
• Regular expression syntax
• Namespaces ::
• === operator

Other features

• Functional: take, zip, reduce, map
• Introspection: class, methods
• Interactive environment irb
• Multi-line comments =begin =end
• Statement modifiers (if, unless)
• yield, break

More info