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 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
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
A new instance of Contract.
-
#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.
-
#maybe_append_options!(args, blk) ⇒ Object
Same thing for when we have named params but didn’t pass any in.
-
#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
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) @has_proc_contract = is_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 178 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 146 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 206 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 225 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 do |arg| return false unless arg.is_a?(Array) && arg.length == contract.length arg.zip(contract).all? do |_arg, _contract| Contract.valid?(_arg, _contract) end end elsif klass == Hash # e.g. { :a => Num, :b => String } lambda do |arg| return false unless arg.is_a?(Hash) contract.keys.all? do |k| Contract.valid?(arg[k], contract[k]) end end elsif klass == Contracts::Args lambda do |arg| Contract.valid?(arg, contract.contract) end elsif klass == Contracts::Func lambda do |arg| arg.is_a?(Method) || arg.is_a?(Proc) end 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 197 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 202 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 217 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 269 def [](*args, &blk) call(*args, &blk) end |
#call(*args, &blk) ⇒ Object
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# File 'lib/contracts.rb', line 273 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 299 def call_with(this, *args, &blk) args << blk if blk # Explicitly append blk=nil if nil != Proc contract violation anticipated maybe_append_block!(args, blk) # Explicitly append options={} if Hash contract is present (args, blk) # Loop forward validating the arguments up to the splat (if there is one) (@args_contract_index || args.size).times do |i| contract = args_contracts[i] arg = args[i] validator = @args_validators[i] unless validator && validator[arg] return unless Contract.failure_callback(:arg => arg, :contract => contract, :class => klass, :method => method, :contracts => self, :arg_pos => i+1, :total_args => args.size, :return_value => false) end if contract.is_a?(Contracts::Func) args[i] = Contract.new(klass, arg, *contract.contracts) end end # If there is a splat loop backwards to the lower index of the splat # Once we hit the splat in this direction set its upper index # Keep validating but use this upper index to get the splat validator. if @args_contract_index splat_upper_index = @args_contract_index (args.size - @args_contract_index).times do |i| arg = args[args.size - 1 - i] if args_contracts[args_contracts.size - 1 - i].is_a?(Contracts::Args) splat_upper_index = i end # Each arg after the spat is found must use the splat validator j = i < splat_upper_index ? i : splat_upper_index contract = args_contracts[args_contracts.size - 1 - j] validator = @args_validators[args_contracts.size - 1 - j] unless validator && validator[arg] return unless Contract.failure_callback(:arg => arg, :contract => contract, :class => klass, :method => method, :contracts => self, :arg_pos => i-1, :total_args => args.size, :return_value => false) end if contract.is_a?(Contracts::Func) args[args.size - 1 - i] = Contract.new(klass, arg, *contract.contracts) end end end # If we put the block into args for validating, restore the args args.slice!(-1) if blk 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 389 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 283 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 290 def 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 399 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 404 def pattern_match? @pattern_match end |
#pretty_contract(c) ⇒ Object
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# File 'lib/contracts.rb', line 133 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 137 def to_s args = args_contracts.map { |c| pretty_contract(c) }.join(", ") ret = pretty_contract(ret_contract) ("#{args} => #{ret}").gsub("Contracts::", "") end |