Class: Contract
- Inherits:
-
Contracts::Decorator
- Object
- Contracts::Decorator
- Contract
- 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.
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.new do |data| raise data[:contracts].failure_exception.new(failure_msg(data), data) end
Instance Attribute Summary collapse
-
#args_contracts ⇒ Object
readonly
Returns the value of attribute args_contracts.
-
#klass ⇒ Object
readonly
Returns the value of attribute klass.
-
#method ⇒ Object
readonly
Returns the value of attribute method.
-
#ret_contract ⇒ Object
readonly
Returns the value of attribute ret_contract.
Class Method Summary collapse
-
.failure_callback(data, use_pattern_matching = true) ⇒ Object
Callback for when a contract fails.
-
.failure_msg(data) ⇒ Object
Given a hash, prints out a failure message.
- .fetch_failure_callback ⇒ Object
-
.make_validator(contract) ⇒ Object
This is a little weird.
-
.override_failure_callback(&blk) ⇒ Object
Used to override failure_callback without monkeypatching.
-
.restore_failure_callback ⇒ Object
Used to restore default failure callback.
-
.valid?(arg, contract) ⇒ Boolean
Used to verify if an argument satisfies a contract.
Instance Method Summary collapse
- #[](*args, &blk) ⇒ Object
- #call(*args, &blk) ⇒ Object
- #call_with(this, *args, &blk) ⇒ Object
-
#failure_exception ⇒ Object
Used to determine type of failure exception this contract should raise in case of failure.
-
#initialize(klass, method, *contracts) ⇒ Contract
constructor
decorator_name :contract.
-
#pattern_match! ⇒ Object
Used internally to mark contract as pattern matching contract.
-
#pattern_match? ⇒ Boolean
Used to determine if contract is a pattern matching contract.
- #pretty_contract(c) ⇒ Object
- #to_s ⇒ Object
Methods inherited from Contracts::Decorator
Constructor Details
#initialize(klass, method, *contracts) ⇒ Contract
decorator_name :contract
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# File 'lib/contracts.rb', line 74 def initialize(klass, method, *contracts) if contracts[-1].is_a? Hash # 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 @ret_validator = Contract.make_validator(@ret_contract) else fail "It looks like your contract for #{method} doesn't have a return value. A contract should be written as `Contract arg1, arg2 => return_value`." end @klass, @method= klass, method @has_func_contracts = args_contracts.index do |contract| contract.is_a? Contracts::Func end end |
Instance Attribute Details
#args_contracts ⇒ Object (readonly)
Returns the value of attribute args_contracts.
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# File 'lib/contracts.rb', line 72 def args_contracts @args_contracts end |
#klass ⇒ Object (readonly)
Returns the value of attribute klass.
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# File 'lib/contracts.rb', line 72 def klass @klass end |
#method ⇒ Object (readonly)
Returns the value of attribute method.
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# File 'lib/contracts.rb', line 72 def method @method end |
#ret_contract ⇒ Object (readonly)
Returns the value of attribute ret_contract.
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# File 'lib/contracts.rb', line 72 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 142 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 105 def self.failure_msg(data) expected = if data[:contract].to_s == "" || data[:contract].is_a?(Hash) data[:contract].inspect else data[:contract].to_s end 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 170 def self.fetch_failure_callback @failure_callback ||= DEFAULT_FAILURE_CALLBACK end |
.make_validator(contract) ⇒ Object
This is a little weird. For each contract we pre-make a proc to validate it so we don’t have to go through this decision tree every time. Seems silly but it saves us a bunch of time (4.3sec vs 5.2sec)
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# File 'lib/contracts.rb', line 189 def self.make_validator(contract) # if is faster than case! klass = contract.class if klass == Proc # e.g. lambda {true} contract elsif klass == Array # e.g. [Num, String] # TODO account for these errors too lambda { |arg| return false unless arg.is_a?(Array) && arg.length == contract.length arg.zip(contract).all? do |_arg, _contract| Contract.valid?(_arg, _contract) end } elsif klass == Hash # e.g. { :a => Num, :b => String } lambda { |arg| return false unless arg.is_a?(Hash) contract.keys.all? do |k| Contract.valid?(arg[k], contract[k]) end } elsif klass == Contracts::Args lambda { |arg| Contract.valid?(arg, contract.contract) } elsif klass == Contracts::Func lambda { |arg| arg.is_a?(Method) || arg.is_a?(Proc) } else # classes and everything else # e.g. Fixnum, Num if contract.respond_to? :valid? lambda { |arg| contract.valid?(arg) } elsif klass == Class lambda { |arg| arg.is_a?(contract) } else lambda { |arg| contract == arg } end end 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 161 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 166 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.
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# File 'lib/contracts.rb', line 181 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 233 def [](*args, &blk) call(*args, &blk) end |
#call(*args, &blk) ⇒ Object
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# File 'lib/contracts.rb', line 237 def call(*args, &blk) call_with(nil, *args, &blk) end |
#call_with(this, *args, &blk) ⇒ Object
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# File 'lib/contracts.rb', line 241 def call_with(this, *args, &blk) _args = blk ? args + [blk] : args size = @args_contracts.size last_contract = @args_contracts.last proc_present = (Contracts::Func === last_contract || (Class === last_contract && (last_contract <= Proc || last_contract <= Method))) _splat_index = proc_present ? -2 : -1 splat_present = Contracts::Args === @args_contracts[_splat_index] splat_index = size + _splat_index splat_index += 1 unless splat_present # Explicitly append blk=nil if nil != Proc contract violation # anticipated if proc_present && !blk && (splat_present || _args.size < size) _args << nil end # Size of our iteration is either count of arguments or count of # contracts. Without splat - count of arguments, with splat - # min(count of contracts, count of arguments) _size = _args.size iteration_size = _size iteration_size = size if !splat_present && size < _size # check contracts on arguments # fun fact! This is significantly faster than .zip (3.7 secs vs 4.7 secs). Why?? # times is faster than (0..args.size).each iteration_size.times do |i| # this is done to account for extra args (for *args) j = i > splat_index ? splat_index : i j = size - 1 if i == _size - 1 && proc_present #unless true #@args_contracts[i].valid?(args[i]) unless @args_validators[j][_args[i]] call_function = Contract.failure_callback({:arg => _args[i], :contract => @args_contracts[j], :class => @klass, :method => @method, :contracts => self, :arg_pos => i+1, :total_args => _size}) return unless call_function end end if @has_func_contracts # contracts on methods contracts_size = @args_contracts.size @args_contracts.each_with_index do |contract, i| next if contracts_size - 1 == i && proc_present && blk if contract.is_a?(Contracts::Func) args[i] = Contract.new(@klass, args[i], *contract.contracts) end end if proc_present && blk && last_contract.is_a?(Contracts::Func) blk_contract = Contract.new(@klass, blk, *last_contract.contracts) blk = Proc.new { |*args, &blk| blk_contract.call(*args, &blk) } end end result = if @method.respond_to?(:call) # proc, block, lambda, etc @method.call(*args, &blk) else # original method name referrence @method.send_to(this, *args, &blk) end unless @ret_validator[result] Contract.failure_callback({:arg => result, :contract => @ret_contract, :class => @klass, :method => @method, :contracts => self, :return_value => true}) end this.verify_invariants!(@method) if this.respond_to?(:verify_invariants!) result 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 318 def failure_exception if @pattern_match PatternMatchingError else ContractError end end |
#pattern_match! ⇒ Object
Used internally to mark contract as pattern matching contract
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# File 'lib/contracts.rb', line 328 def pattern_match! @pattern_match = true end |
#pattern_match? ⇒ Boolean
Used to determine if contract is a pattern matching contract
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# File 'lib/contracts.rb', line 333 def pattern_match? @pattern_match end |
#pretty_contract(c) ⇒ Object
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# File 'lib/contracts.rb', line 92 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 96 def to_s args = @args_contracts.map { |c| pretty_contract(c) }.join(", ") ret = pretty_contract(@ret_contract) ("#{args} => #{ret}").gsub("Contracts::", "") end |