Ruby, adding multiple objects to an array at once

Question

I have Shop class, and I want to add multiple items at once. I want this:

shop1 = Shop.new
product1 = Product.new("Dress", 50)
shop1.add_products(product1, 5)

to add 5 dresses to warehouse

def add(product, qty)
  @products << product * qty
end

so later I can use

@products.select{|p| p.name == "Dress"}.count

and get 5. Is it possible?

Be careful, though: when you do [item] * 3, you get an array of three references to the same item, not three items. Altering any of them will affect all the array items. — Mladen Jablanović
– Mladen Jablanović, Commented Jul 6, 2016 at 13:49

Albin · Accepted Answer · 2016-07-06 10:55:03Z

3

The easiest way I think is:

def add(product, qty)
  @products += [product] * qty
end

But it all comes down to your syntax preferences.

answered Jul 6, 2016 at 10:55

Albin

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1 Comment

Arne Brasseur Over a year ago

The difference with the concat version is that this one creates a new array, instead of adding to the existing one. They're both valid ways to do it. I did an in-place edit because that's what the OP did as well.

Arne Brasseur · Accepted Answer · 2016-07-06 10:48:24Z

3

You could do something like this

def add(product, qty)
  @products.concat([product] * qty)
end

or less "clever"

def add(product, qty)
  qty.times { @products << product }
end

answered Jul 6, 2016 at 10:48

Arne Brasseur

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Comments

BrunoF · Accepted Answer · 2016-07-06 12:09:14Z

Both previous answers will solve your problem. However, maybe you should consider using a hash instead of an array.

Something like this:

 class Product    
  @@products = Hash.new(0)

  def initialize(product, qty)
    @@products[product] = qty
  end

  def increase_stock(product, qty)
    @@products[product] += qty
  end

  def decrease_stock(product, qty)
    @@products[product] -= qty
  end

  def count_stock(product)
    @@products[product]
  end
end

p = Product.new('Dress',5)
p.count_stock('Dress')
 => 5
p.increase_stock('Dress',10)
p.count_stock('Dress')
 => 15
p.decrease_stock('Dress',2)
p.count_stock('Dress')
 => 13

In my GitHub, there is a simple command-line inventory management app written in Ruby. May be useful..

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