Simplecheck

Simplecheck is a lightweight property checking API for Ruby designed to quickly check arguments in under 50 lines of Ruby. Once included into a class it provides the check instance method which takes arguments and a condition to check them against.

If a check fails a Simplecheck::CheckFailed exception is raised.

Simplecheck is compatiable with Ruby 2.0.0 and above only.

Installation

Simplecheck is available as a Rubygem installable via gem install simplecheck.

A git repository is also available at http://github.com/farrel/simplecheck.

Usage

require 'simplecheck'

class Customer
  include Simplecheck

  attr_accessor( :name, :age )

  def initialize( name, age )
    check(name, String, error_message: 'name must be a String') # Check name is String with custom error message
    check(age, 18..75)                                          # Check age is within Range

    @name, @age = name, age
  end
end

Customer.new("Joe", 25) # No error

begin
  Customer.new(nil, 25)
rescue Simplecheck::CheckFailed => exception
  puts exception.message # => 'name must be a String'  
ebd

begin 
  Customer.new("Joe", 15) 
rescue Simplecheck::CheckFailed => exception
  puts exception.message # => '15 does not satisfy 18..75'
ebd

Check Methods

Simplecheck currently supports three different check methods:

  • Expression Check
  • Case Equality (===) Check
  • Block Check

Custom Error Message

All check methods may take an optional named parameter error_message to override the default error message.

check(age, Integer, error_message: 'Age must be an whole number')

Expression Check

In the simplest case check takes an expression as an argument. If the expression evaluates to nil or false it will fail. 

def calculate_percentage( score, total )
  check(total > 0)
  100.0 * score / total
end

Case Equality (===) Check

If two or more arguments are given without a block, then the last argument becomes the condition against which the previous arguments are checked. To accomplish this the condition argument should implement the case equality operator (=== or threequal) in a logical manner.

def greatest_common_divisor(a, b)
  check(a, b, Integer)
  # GCD Algorithm...
end

If a class does not alias or implement it's own version of === it has the same functionality as ==. The following Ruby Core classes already alias === to various instance methods.

Class

=== is aliased to kind_of?:

check(age, Numeric)

Range

=== is aliased to include?:

check(age, 18..75)

Regexp

=== is aliased to =~:

check(phone_number, /^\d\d\d-\d\d\d\d$/)

Proc

=== is aliased to call: 

check(password, password_confirmation , ->(p) { !Dict.lookup(p) })

Custom Check Object

The default behaviour of Object#=== is the same as Object#==. To customise the behaviour implement your own Object#=== method.

For example to check whether a set of points is inside a given polygon we would implement Polygon#=== as a point-in-polygon algorithm, allowing us to carry out the check using a Polygon instance:

check(point_1, point_2, polygon)

Block Check

A block can be passed to check, with the arguments passed to check then passed individually to the block:

check(a, b, c) do |n|
  n.odd?
end

This is syntactic sugar for the Proc Case Equality check.

Multiple Arguments

Case Equality and Block checks can be called with multiple arguments, with each argument being checked individually against the condition:

check( i, j, k, Integer ) 
check( a, b, c ) do |n|
  n.even?
end

Resources