Class: Plumb::Policies

Inherits:
Object
  • Object
show all
Defined in:
lib/plumb/policies.rb

Overview

A policy registry for Plumb It holds and gets registered policies. Policies are callable objects that act as factories for type compositions.

Constant Summary collapse

UnknownPolicyError = 
Class.new(StandardError)
MethodAlreadyDefinedError = 
Class.new(StandardError)

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Policies

Returns a new instance of Policies.



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# File 'lib/plumb/policies.rb', line 13

def initialize
  @policies = {}
end

Instance Method Details

#get(types, name) ⇒ #call

Get a policy for a given type.

Parameters:

  • types (Array<Class>) —

    the types

  • name (Symbol) —

    the policy name

Returns:

  • (#call) —

    the policy callable

Raises:



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# File 'lib/plumb/policies.rb', line 44

def get(types, name)
  if (pol = resolve_shared_policy(types, name))
    pol
  elsif (pol = @policies.dig(name, Object))
    raise UnknownPolicyError, "Unknown policy #{name} for #{types.inspect}" unless pol

    pol
  else
    raise UnknownPolicyError, "Unknown or incompatible policy #{name} for #{types.inspect}"
  end
end

#register(for_type, name, policy) ⇒ Object

Register a policy for all or specific outpyt types. Example for a policy that works for all types:

#register(Object, :my_policy, ->(node, arg) { ... })

Example for a policy that works for a specific type:

#register(String, :my_policy, ->(node, arg) { ... })

Example for a policy that works for a specific interface:

#register(:size, :my_policy, ->(node, arg) { ... })

The policy callable takes the step it is applied to, a policy argument (if any) and a policy block (if any). Example for a policy #default(default_value = Undefined) { ‘some-default-value’ }

policy = proc do |type, default_value = Undefined, &block|
  type | (Plumb::Types::Undefined >> Plumb::Types::Static[default_value])
end

Parameters:

  • for_type (Class, Symbol) —

    the type the policy is for.

  • name (Symbol) —

    the name of the policy.

  • policy (Proc) —

    the policy to register.



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# File 'lib/plumb/policies.rb', line 34

def register(for_type, name, policy)
  @policies[name] ||= {}
  @policies[name][for_type] = policy
end