Class: Contract

Inherits:
Contracts::Decorator show all
Extended by:
Contracts::Validators
Includes:
Contracts::CallWith
Defined in:
lib/contracts.rb

Overview

This is the main Contract class. When you write a new contract, you’ll write it as:

Contract [contract names] => return_value

This class also provides useful callbacks and a validation method.

For #make_validator and related logic see file lib/contracts/validators.rb For #call_with and related logic see file lib/contracts/call_with.rb

Constant Summary collapse

DEFAULT_FAILURE_CALLBACK =

Default implementation of failure_callback. Provided as a block to be able to monkey patch #failure_callback only temporary and then switch it back. First important usage - for specs.

proc do |data|
  if data[:return_value]
    # this failed on the return contract
    fail ReturnContractError.new(failure_msg(data), data)
  else
    # this failed for a param contract
    fail data[:contracts].failure_exception.new(failure_msg(data), data)
  end
end

Constants included from Contracts::Validators

Contracts::Validators::DEFAULT_VALIDATOR_STRATEGIES

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Contracts::Validators

clean_memoized_validators, make_validator, make_validator!, memoized_validators, override_validator, reset_validators, restore_validators, validator_strategies

Methods included from Contracts::CallWith

#call_with

Methods inherited from Contracts::Decorator

inherited

Constructor Details

#initialize(klass, method, *contracts) ⇒ Contract

Returns a new instance of Contract.



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# File 'lib/contracts.rb', line 86

def initialize(klass, method, *contracts)
  unless contracts.last.is_a?(Hash)
    unless contracts.one?
      fail %{
        It looks like your contract for #{method.name} doesn't have a return
        value. A contract should be written as `Contract arg1, arg2 =>
        return_value`.
      }.strip
    end
    contracts = [nil => contracts[-1]]
  end

  # internally we just convert that return value syntax back to an array
  @args_contracts = contracts[0, contracts.size - 1] + contracts[-1].keys

  @ret_contract = contracts[-1].values[0]

  @args_validators = args_contracts.map do |contract|
    Contract.make_validator(contract)
  end

  @args_contract_index = args_contracts.index do |contract|
    contract.is_a? Contracts::Args
  end

  @ret_validator = Contract.make_validator(ret_contract)

  # == @has_proc_contract
  last_contract = args_contracts.last
  is_a_proc = last_contract.is_a?(Class) && (last_contract <= Proc || last_contract <= Method)
  maybe_a_proc = last_contract.is_a?(Contracts::Maybe) && last_contract.include_proc?

  @has_proc_contract = is_a_proc || maybe_a_proc || last_contract.is_a?(Contracts::Func)
  # ====

  # == @has_options_contract
  last_contract = args_contracts.last
  penultimate_contract = args_contracts[-2]
  @has_options_contract = if @has_proc_contract
                            penultimate_contract.is_a?(Hash)
                          else
                            last_contract.is_a?(Hash)
                          end
  # ===

  @klass, @method = klass, method
end

Instance Attribute Details

#args_contracts ⇒ Object (readonly)

Returns the value of attribute args_contracts.



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# File 'lib/contracts.rb', line 85

def args_contracts
  @args_contracts
end

#klass ⇒ Object (readonly)

Returns the value of attribute klass.



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# File 'lib/contracts.rb', line 85

def klass
  @klass
end

#method ⇒ Object (readonly)

Returns the value of attribute method.



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# File 'lib/contracts.rb', line 85

def method
  @method
end

#ret_contract ⇒ Object (readonly)

Returns the value of attribute ret_contract.



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# File 'lib/contracts.rb', line 85

def ret_contract
  @ret_contract
end

Class Method Details

.failure_callback(data, use_pattern_matching = true) ⇒ Object

Callback for when a contract fails. By default it raises an error and prints detailed info about the contract that failed. You can also monkeypatch this callback to do whatever you want…log the error, send you an email, print an error message, etc.

Example of monkeypatching:

def Contract.failure_callback(data)
  puts "You had an error!"
  puts failure_msg(data)
  exit
end



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# File 'lib/contracts.rb', line 179

def self.failure_callback(data, use_pattern_matching = true)
  if data[:contracts].pattern_match? && use_pattern_matching
    return DEFAULT_FAILURE_CALLBACK.call(data)
  end

  fetch_failure_callback.call(data)
end

.failure_msg(data) ⇒ Object

Given a hash, prints out a failure message. This function is used by the default #failure_callback method and uses the hash passed into the failure_callback method.



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# File 'lib/contracts.rb', line 147

def self.failure_msg(data)
  expected = Contracts::Formatters::Expected.new(data[:contract]).contract
  position = Contracts::Support.method_position(data[:method])
  method_name = Contracts::Support.method_name(data[:method])

  header = if data[:return_value]
             "Contract violation for return value:"
           else
             "Contract violation for argument #{data[:arg_pos]} of #{data[:total_args]}:"
           end

  %{#{header}
      Expected: #{expected},
      Actual: #{data[:arg].inspect}
      Value guarded in: #{data[:class]}::#{method_name}
      With Contract: #{data[:contracts]}
      At: #{position} }
end

.fetch_failure_callback ⇒ Object 



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# File 'lib/contracts.rb', line 207

def self.fetch_failure_callback
  @failure_callback ||= DEFAULT_FAILURE_CALLBACK
end

.override_failure_callback(&blk) ⇒ Object

Used to override failure_callback without monkeypatching.

Takes: block parameter, that should accept one argument - data.

Example usage:

Contract.override_failure_callback do |data|
  puts "You had an error"
  puts failure_msg(data)
  exit
end



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# File 'lib/contracts.rb', line 198

def self.override_failure_callback(&blk)
  @failure_callback = blk
end

.restore_failure_callback ⇒ Object

Used to restore default failure callback



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# File 'lib/contracts.rb', line 203

def self.restore_failure_callback
  @failure_callback = DEFAULT_FAILURE_CALLBACK
end

.valid?(arg, contract) ⇒ Boolean

Used to verify if an argument satisfies a contract.

Takes: an argument and a contract.

Returns: a tuple: [Boolean, metadata]. The boolean indicates whether the contract was valid or not. If it wasn’t, metadata contains some useful information about the failure.

Returns:

  • (Boolean) 


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# File 'lib/contracts.rb', line 218

def self.valid?(arg, contract)
  make_validator(contract)[arg]
end

Instance Method Details

#[](*args, &blk) ⇒ Object 



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# File 'lib/contracts.rb', line 222

def [](*args, &blk)
  call(*args, &blk)
end

#call(*args, &blk) ⇒ Object 



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# File 'lib/contracts.rb', line 226

def call(*args, &blk)
  call_with(nil, *args, &blk)
end

#failure_exception ⇒ Object

Used to determine type of failure exception this contract should raise in case of failure



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# File 'lib/contracts.rb', line 253

def failure_exception
  if @pattern_match
    PatternMatchingError
  else
    ParamContractError
  end
end

#maybe_append_block!(args, blk) ⇒ Object

a better way to handle this might be to take this into account before throwing a “mismatched # of args” error.



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# File 'lib/contracts.rb', line 236

def maybe_append_block! args, blk
  return unless @has_proc_contract && !blk &&
      (@args_contract_index || args.size < args_contracts.size)
  args << nil
end

#maybe_append_options!(args, blk) ⇒ Object

Same thing for when we have named params but didn’t pass any in.



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# File 'lib/contracts.rb', line 243

def maybe_append_options! args, blk
  return unless @has_options_contract
  if @has_proc_contract && args_contracts[-2].is_a?(Hash) && !args[-2].is_a?(Hash)
    args.insert(-2, {})
  elsif args_contracts[-1].is_a?(Hash) && !args[-1].is_a?(Hash)
    args << {}
  end
end

#pattern_match! ⇒ Object

Used internally to mark contract as pattern matching contract



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# File 'lib/contracts.rb', line 263

def pattern_match!
  @pattern_match = true
end

#pattern_match? ⇒ Boolean

Used to determine if contract is a pattern matching contract

Returns:

  • (Boolean) 


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# File 'lib/contracts.rb', line 268

def pattern_match?
  @pattern_match
end

#pretty_contract(c) ⇒ Object 



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# File 'lib/contracts.rb', line 134

def pretty_contract c
  c.is_a?(Class) ? c.name : c.class.name
end

#to_s ⇒ Object 



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# File 'lib/contracts.rb', line 138

def to_s
  args = args_contracts.map { |c| pretty_contract(c) }.join(", ")
  ret = pretty_contract(ret_contract)
  ("#{args} => #{ret}").gsub("Contracts::", "")
end