SingletonAttribute

#region license // Copyright (c) 2005, Sorin Ionescu // All rights reserved. // // Redistribution and use in source and binary forms, with or without modification, // are permitted provided that the following conditions are met: // // * Redistributions of source code must retain the above copyright notice, // this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above copyright notice, // this list of conditions and the following disclaimer in the documentation // and/or other materials provided with the distribution. // * Neither the name of Sorin Ionescu nor the names of its // contributors may be used to endorse or promote products derived from this // software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED // WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF // THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #endregion

namespace Boo.Lang.Useful.Attributes

import Boo.Lang.Compiler import Boo.Lang.Compiler.Ast

class SingletonAttribute(AbstractAstAttribute): """ Implements the singleton pattern for a class.

@author Sorin Ionescu @author Rodrigo B. de Oliveira """ _singletonType as ClassDefinition _instance as ReferenceExpression _singletonLock as ReferenceExpression

def constructor():
	pass
	
override def Apply(node as Node):
	assert node isa ClassDefinition
	
	_singletonType = node as ClassDefinition

	MakeClassFinal()
	MakeConstructorsPrivate()
	CreateInstanceField()
	CreateSingletonLockField()
	CreateInstanceProperty()

private def MakeClassFinal():
	_singletonType.Modifiers |= TypeMemberModifiers.Final

private def MakeConstructorsPrivate():
	for member in _singletonType.Members:
		ctor = member as Constructor
		
		if ctor is not null:
			ctor.Modifiers |= TypeMemberModifiers.Private
			ctorFound = true
	
	if not ctorFound:
		_singletonType.Members.Add(
			Constructor(
				LexicalInfo: LexicalInfo,
				Modifiers: TypeMemberModifiers.Private))
				
private def CreateInstanceField():
	instance = Field(
		LexicalInfo: LexicalInfo,
		Name: "___instance",
		Modifiers: TypeMemberModifiers.Private | TypeMemberModifiers.Static,
		Type: SimpleTypeReference(_singletonType.Name))
	
	_instance = ReferenceExpression(instance.Name)
	
	_singletonType.Members.Add(instance)

private def CreateSingletonLockField():
	singletonLock  = Field(
		LexicalInfo: LexicalInfo,
		Name: "___singletonLock",
		Modifiers: TypeMemberModifiers.Private | TypeMemberModifiers.Static,
		Type: SimpleTypeReference("object"),
		Initializer: MethodInvocationExpression(
			ReferenceExpression("object")))
	
	_singletonLock = ReferenceExpression(singletonLock.Name)
	
	_singletonType.Members.Add(singletonLock)

private def CreateInstanceProperty():
	instanceProperty = Property(
		LexicalInfo: LexicalInfo,
		Name: "Instance",
		Modifiers: TypeMemberModifiers.Public | TypeMemberModifiers.Static,
		Type: SimpleTypeReference(_singletonType.Name))
	
	instanceGetter = instanceProperty.Getter = Method(
		LexicalInfo,
		Name: "get")
		
	instanceCreation = MethodInvocationExpression(
		LexicalInfo: LexicalInfo,
		Target: AstUtil.CreateReferenceExpression(_singletonType.FullName))
	
	instanceAssignment = BinaryExpression(
		LexicalInfo,
		BinaryOperatorType.Assign,
		_instance.CloneNode(),
		instanceCreation)
		
	ifInstanceNullOne = IfStatement(
		LexicalInfo,
		BinaryExpression(
			LexicalInfo,
			BinaryOperatorType.Equality,
			_instance.CloneNode(),
			NullLiteralExpression(LexicalInfo)),
		Block(LexicalInfo), null)
	
	ifInstanceNullTwo = IfStatement(
		LexicalInfo,
		BinaryExpression(
			LexicalInfo,
			BinaryOperatorType.Equality,
			_instance.CloneNode(),
			NullLiteralExpression(LexicalInfo)),
		Block(LexicalInfo), null)

	ifInstanceNullTwo.TrueBlock.Add(instanceAssignment)
	
	lockMacro = MacroStatement(LexicalInfo: LexicalInfo, Name: "lock")
	lockMacro.Arguments.Add(_singletonLock)
	lockMacro.Block.Add(ifInstanceNullTwo)                       		
	
	ifInstanceNullOne.TrueBlock.Add(lockMacro)
	
	instanceGetter.Body.Add(ifInstanceNullOne)
	instanceGetter.Body.Add(
		ReturnStatement(
			LexicalInfo: LexicalInfo,
			Expression: _instance.CloneNode()))
	
	_singletonType.Members.Add(instanceProperty)