Blocks and Methods

Block Parameters

Blocks receive parameters and can make local calculations for each yielded value.

block parameter Names between vertical bars receive values from the method that is running the block.

Block Parameters

multiplier
block_parameters.rb
Replay: real traced execution (multi-file project)
numbers = [2, 4, 6]
multiplier = 3

numbers.each do |number|
  product = number * multiplier
  puts "#{number}x#{multiplier}=#{product}"
end

numbers = [2, 4, 6]
multiplier = 2

numbers.each do |number|
  product = number * multiplier
  puts "#{number}x#{multiplier}=#{product}"
end

numbers = [2, 4, 6]
multiplier = 5

numbers.each do |number|
  product = number * multiplier
  puts "#{number}x#{multiplier}=#{product}"
end

  1. numbers ← [2, 4, 6], multiplier ← 3

    1numbers→ [2, 4, 6] = [2, 4, 6]2multiplier→ 3 = 3  #@multiplier=2, 534numbers[2, 4, 6].each do |number|5  product = number * multiplier6  puts "#{number}x#{multiplier}=#{product}"7end

  2. product ← 6

    pass 1 of 3
    4numbers.each do |number2|5  product→ 6 = number2 * multiplier36  puts "#{number2}x#{multiplier3}=#{product6}"7end
    output2x3=6
    All 3 passes — pass 1 is the card above
    passnumbernumbersproduct
    12—6
    24—12
    36[2, 4, 6]18

  1. numbers ← [2, 4, 6], multiplier ← 2

    1numbers→ [2, 4, 6] = [2, 4, 6]2multiplier→ 2 = 234numbers[2, 4, 6].each do |number|5  product = number * multiplier6  puts "#{number}x#{multiplier}=#{product}"7end

  2. product ← 4

    pass 1 of 3
    4numbers.each do |number2|5  product→ 4 = number2 * multiplier26  puts "#{number2}x#{multiplier2}=#{product4}"7end
    output2x2=4
    All 3 passes — pass 1 is the card above
    passnumbernumbersproduct
    12—4
    24—8
    36[2, 4, 6]12

  1. numbers ← [2, 4, 6], multiplier ← 5

    1numbers→ [2, 4, 6] = [2, 4, 6]2multiplier→ 5 = 534numbers[2, 4, 6].each do |number|5  product = number * multiplier6  puts "#{number}x#{multiplier}=#{product}"7end

  2. product ← 10

    pass 1 of 3
    4numbers.each do |number2|5  product→ 10 = number2 * multiplier56  puts "#{number2}x#{multiplier5}=#{product10}"7end
    output2x5=10
    All 3 passes — pass 1 is the card above
    passnumbernumbersproduct
    12—10
    24—20
    36[2, 4, 6]30

Follow the Parameters

  1. numbers starts as 2, 4, and 6.
  2. multiplier starts as 3.
  3. Each block run receives one number.
  4. The block multiplies that number by 3 and prints the equation. | number | multiplier | product | output | | --- | --- | --- | --- | | 2 | 3 | 6 | 2x3=6 | | 4 | 3 | 12 | 4x3=12 | | 6 | 3 | 18 | 6x3=18 |

Exercise: block_parameters.rb

Reproduce the three default equations, then use the pinned multiplier variants to predict the products for 2 and 5.