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


54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
# File 'lib/contracts.rb', line 54

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)

  @pattern_match = false

  # == @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) || penultimate_contract.is_a?(Contracts::Builtin::KeywordArgs)
                          else
                            last_contract.is_a?(Hash) || last_contract.is_a?(Contracts::Builtin::KeywordArgs)
                          end
  # ===

  @klass, @method = klass, method
end

Instance Attribute Details

#args_contractsObject (readonly)

Returns the value of attribute args_contracts


53
54
55
# File 'lib/contracts.rb', line 53

def args_contracts
  @args_contracts
end

#klassObject (readonly)

Returns the value of attribute klass


53
54
55
# File 'lib/contracts.rb', line 53

def klass
  @klass
end

#methodObject (readonly)

Returns the value of attribute method


53
54
55
# File 'lib/contracts.rb', line 53

def method
  @method
end

#ret_contractObject (readonly)

Returns the value of attribute ret_contract


53
54
55
# File 'lib/contracts.rb', line 53

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

150
151
152
153
154
155
156
# File 'lib/contracts.rb', line 150

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.


118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
# File 'lib/contracts.rb', line 118

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_callbackObject


178
179
180
# File 'lib/contracts.rb', line 178

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

169
170
171
# File 'lib/contracts.rb', line 169

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

.restore_failure_callbackObject

Used to restore default failure callback


174
175
176
# File 'lib/contracts.rb', line 174

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.


189
190
191
# File 'lib/contracts.rb', line 189

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

Instance Method Details

#[](*args, &blk) ⇒ Object


193
194
195
# File 'lib/contracts.rb', line 193

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

#call(*args, &blk) ⇒ Object


197
198
199
# File 'lib/contracts.rb', line 197

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

#failure_exceptionObject

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


228
229
230
231
232
233
234
# File 'lib/contracts.rb', line 228

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. returns true if it appended nil


208
209
210
211
212
213
# File 'lib/contracts.rb', line 208

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

#maybe_append_options!(args, blk) ⇒ Object

Same thing for when we have named params but didn't pass any in. returns true if it appended nil


217
218
219
220
221
222
223
224
225
# File 'lib/contracts.rb', line 217

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

#pattern_match!Object

Used internally to mark contract as pattern matching contract


238
239
240
# File 'lib/contracts.rb', line 238

def pattern_match!
  @pattern_match = true
end

#pattern_match?Boolean

Used to determine if contract is a pattern matching contract


243
244
245
# File 'lib/contracts.rb', line 243

def pattern_match?
  @pattern_match == true
end

#pretty_contract(c) ⇒ Object


105
106
107
# File 'lib/contracts.rb', line 105

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

#to_sObject


109
110
111
112
113
# File 'lib/contracts.rb', line 109

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