Module: Fiddle::CStructBuilder

Defined in:
lib/fiddle/struct.rb

Overview

Used to construct C classes (CUnion, CStruct, etc)

Fiddle::Importer#struct and Fiddle::Importer#union wrap this functionality in an easy-to-use manner.

Class Method Summary collapse

Class Method Details

.create(klass, types, members) ⇒ Object

Construct a new class given a C:

  • class klass (CUnion, CStruct, or other that provide an #entity_class)

  • types (Fiddle::TYPE_INT, Fiddle::TYPE_SIZE_T, etc., see the C types constants)

  • corresponding members

Fiddle::Importer#struct and Fiddle::Importer#union wrap this functionality in an easy-to-use manner.

Examples:

require 'fiddle/struct'
require 'fiddle/cparser'

include Fiddle::CParser

types, members = parse_struct_signature(['int i','char c'])

MyStruct = Fiddle::CStructBuilder.create(Fiddle::CUnion, types, members)

MyStruct.malloc(Fiddle::RUBY_FREE) do |obj|
  ...
end

obj = MyStruct.malloc(Fiddle::RUBY_FREE)
begin
  ...
ensure
  obj.call_free
end

obj = MyStruct.malloc
begin
  ...
ensure
  Fiddle.free obj.to_ptr
end



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# File 'lib/fiddle/struct.rb', line 215

def create(klass, types, members)
  new_class = Class.new(klass){
    define_method(:initialize){|addr, func = nil|
      if addr.is_a?(self.class.entity_class)
        @entity = addr
      else
        @entity = self.class.entity_class.new(addr, types, func)
      end
      @entity.assign_names(members)
    }
    define_method(:[]) { |*args| @entity.send(:[], *args) }
    define_method(:[]=) { |*args| @entity.send(:[]=, *args) }
    define_method(:to_ptr){ @entity }
    define_method(:to_i){ @entity.to_i }
    define_singleton_method(:types) { types }
    define_singleton_method(:members) { members }

    # Return the offset of a struct member given its name.
    # For example:
    #
    #     MyStruct = struct [
    #       "int64_t i",
    #       "char c",
    #     ]
    #
    #     MyStruct.offsetof("i") # => 0
    #     MyStruct.offsetof("c") # => 8
    #
    define_singleton_method(:offsetof) { |name|
      klass.offsetof(name, members, types)
    }
    members.each{|name|
      name = name[0] if name.is_a?(Array) # name is a nested struct
      next if method_defined?(name)
      define_method(name){ @entity[name] }
      define_method(name + "="){|val| @entity[name] = val }
    }
    entity_class = klass.entity_class
    alignment = entity_class.alignment(types)
    size = entity_class.size(types)
    define_singleton_method(:alignment) { alignment }
    define_singleton_method(:size) { size }
    define_singleton_method(:malloc) do |func=nil, &block|
      if block
        entity_class.malloc(types, func, size) do |entity|
          block.call(new(entity))
        end
      else
        new(entity_class.malloc(types, func, size))
      end
    end
  }
  return new_class
end