# paulfioravanti's solution

## to Circular Buffer in the Ruby Track

Published at May 20 2019 · 0 comments
Instructions
Test suite
Solution

A circular buffer, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end.

A circular buffer first starts empty and of some predefined length. For example, this is a 7-element buffer:

``````[ ][ ][ ][ ][ ][ ][ ]
``````

Assume that a 1 is written into the middle of the buffer (exact starting location does not matter in a circular buffer):

``````[ ][ ][ ][1][ ][ ][ ]
``````

Then assume that two more elements are added — 2 & 3 — which get appended after the 1:

``````[ ][ ][ ][1][2][3][ ]
``````

If two elements are then removed from the buffer, the oldest values inside the buffer are removed. The two elements removed, in this case, are 1 & 2, leaving the buffer with just a 3:

``````[ ][ ][ ][ ][ ][3][ ]
``````

If the buffer has 7 elements then it is completely full:

``````[6][7][8][9][3][4][5]
``````

When the buffer is full an error will be raised, alerting the client that further writes are blocked until a slot becomes free.

When the buffer is full, the client can opt to overwrite the oldest data with a forced write. In this case, two more elements — A & B — are added and they overwrite the 3 & 4:

``````[6][7][8][9][A][B][5]
``````

3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer. Finally, if two elements are removed then what would be returned is 5 & 6 yielding the buffer:

``````[ ][7][8][9][A][B][ ]
``````

Because there is space available, if the client again uses overwrite to store C & D then the space where 5 & 6 were stored previously will be used not the location of 7 & 8. 7 is still the oldest element and the buffer is once again full.

``````[D][7][8][9][A][B][C]
``````

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

``````gem install minitest
``````

If you would like color output, you can `require 'minitest/pride'` in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

``````ruby circular_buffer_test.rb
``````

To include color from the command line:

``````ruby -r minitest/pride circular_buffer_test.rb
``````

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### circular_buffer_test.rb

``````require 'minitest/autorun'
require_relative 'circular_buffer'

class CircularBufferTest < Minitest::Test
buffer = CircularBuffer.new(1)
end

skip
buffer = CircularBuffer.new(1)
buffer.write '1'
end

skip
buffer = CircularBuffer.new(2)
buffer.write '1'
buffer.write '2'
end

def test_clearing_buffer
skip
buffer = CircularBuffer.new(3)
('1'..'3').each { |i| buffer.write i }
buffer.clear
buffer.write '1'
buffer.write '2'
buffer.write '3'
end

skip
buffer = CircularBuffer.new(2)
buffer.write '1'
buffer.write '2'
end

skip
buffer = CircularBuffer.new(3)
buffer.write '1'
buffer.write '2'
buffer.write '3'
end

def test_writing_to_a_full_buffer_throws_an_exception
skip
buffer = CircularBuffer.new(2)
buffer.write '1'
buffer.write '2'
assert_raises(CircularBuffer::BufferFullException) { buffer.write 'A' }
end

def test_overwriting_oldest_item_in_a_full_buffer
skip
buffer = CircularBuffer.new(2)
buffer.write '1'
buffer.write '2'
buffer.write! 'A'
end

def test_forced_writes_to_non_full_buffer_should_behave_like_writes
skip
buffer = CircularBuffer.new(2)
buffer.write '1'
buffer.write! '2'
end

skip
buffer = CircularBuffer.new(5)
('1'..'3').each { |i| buffer.write i }
buffer.write '4'
('5'..'8').each { |i| buffer.write i }
buffer.write! 'A'
buffer.write! 'B'
('6'..'8').each do |i|
end
end
end``````
``````# frozen_string_literal: true

require "forwardable"

class CircularBuffer
class BufferEmptyException < StandardError; end
class BufferFullException < StandardError; end

extend Forwardable

def initialize(size)
@buffer = []
@size = size
end

def_delegators :@buffer, :clear, :empty?, :length, :push, :shift

raise BufferEmptyException if empty?

shift
end

def write(char)
raise BufferFullException if full?

push(char)
end

def write!(char)
write(char)
end

private

def full?
length == size
end
end``````