samples/iyi/inventory.iyi

# The first program with a struct in it - what a person writes in the second
# half hour, after `basics`.
#
#   ./bin/iyi run samples/iyi/inventory.iyi
#
# A record type, a list of them, and the questions a list gets asked: which
# ones, how many, the largest, each with its number, and the same list by
# name. Like `basics`, this documents no rule. It is here because the prelude
# grows only when a program in this repository needs something (SPEC.md 0.1.0
# item 3), and these are the calls the second program makes that the first
# did not.
module samples/inventory

struct Item
  property name : String
  property price : Float64
  property quantity : Int32

  def initialize(@name : String, @price : Float64, @quantity : Int32)
  end

  def total : Float64
    price * quantity
  end
end

items = [
  Item.new("apple", 0.5, 10),
  Item.new("pear", 0.75, 4),
  Item.new("melon", 3.0, 1),
]

# 1. A total, and a subset.
grand = 0.0
items.each { |item| grand += item.total }
puts "total: #{grand}" # => total: 11.0
cheap = items.select { |item| item.price < 1.0 }
puts "cheap: #{cheap.map(&.name).join(", ")}" # => cheap: apple, pear

# 2. Questions with one answer.
puts items.count { |item| item.quantity > 1 } # => 2
puts items.any? { |item| item.price > 2.0 }   # => true
puts items.all? { |item| item.quantity > 0 }  # => true
puts items.max_by { |item| item.price }.name  # => melon
puts items.min_by { |item| item.total }.name  # => pear, the first of equals
if pear = items.find { |item| item.name == "pear" }
  puts pear.total # => 3.0
end
puts items.find { |item| item.name == "plum" }.inspect # => nil

# 3. A report, each line numbered.
items.each_with_index do |item, index|
  puts "#{index + 1}. #{item.name.ljust(6)} #{item.quantity.to_s.rjust(3)}  #{item.total}"
end
# => 1. apple   10  5.0
# => 2. pear     4  3.0
# => 3. melon    1  3.0

# 4. The same items by name.
by_name = {} of String => Item
items.each { |item| by_name[item.name] = item }
puts by_name.keys                       # => ["apple", "pear", "melon"]
puts by_name.values.map(&.quantity).sum # => 15
puts by_name.keys.sorted.last           # => pear