From 62c69c568763b47904f299fa2aecfa017bd71879 Mon Sep 17 00:00:00 2001
From: Henrik Tidefelt <tidefelt@isy.liu.se>
Date: Fri, 14 Nov 2008 16:09:24 +0100
Subject: [PATCH] Helper class for Structure creation in the kernel:
 Kernel::StructureFactory.

This will soon be used by the Schur decomposition function, which will serve as example on how to use the factory.

Basically, the idea is that a global instance of Kernel::StructureFactory is created for each structure signature.  To create an instance of that structure, use the <set> method to modify the fields held in the factory, and when all fields are set, use the <build> method to create an instance.  This is very non-functional, but pretty convenient.  The danger is that one must not forget to set any fields before calling <build>, or values from the last <build> will be used without warning.  Means to prevent this, such as clearing values after every <build>, and checking for unset values upon <build>, seems overly protective and costly.

At least, the factory ensures that only declared fields are assigned, and it takes care of the not-so-obvious details of how to set up a new instance of Lang::Structure.
---
 source/containertypes.cc | 87 ++++++++++++++++++++++++++++++++++++++++++++++++
 source/containertypes.h  | 19 +++++++++++
 2 files changed, 106 insertions(+)

diff --git a/source/containertypes.cc b/source/containertypes.cc
index 6b09db97..ffdb3e4f 100644
--- a/source/containertypes.cc
+++ b/source/containertypes.cc
@@ -512,3 +512,90 @@ Lang::Structure::gcMark( Kernel::GCMarkedSet & marked )
 	const_cast< Lang::SingleList * >( values_.getPtr( ) )->gcMark( marked );
 }
 
+
+Kernel::StructureFactory::StructureFactory( const std::list< const char * > & fields )
+{
+	init( fields );
+}
+
+Kernel::StructureFactory::StructureFactory( const char * field1 )
+{
+	std::list< const char * > fields;
+	fields.push_back( field1 );
+	init( fields );
+}
+
+Kernel::StructureFactory::StructureFactory( const char * field1, const char * field2 )
+{
+	std::list< const char * > fields;
+	fields.push_back( field1 );
+	fields.push_back( field2 );
+	init( fields );
+}
+
+Kernel::StructureFactory::StructureFactory( const char * field1, const char * field2, const char * field3 )
+{
+	std::list< const char * > fields;
+	fields.push_back( field1 );
+	fields.push_back( field2 );
+	fields.push_back( field3 );
+	init( fields );
+}
+
+Kernel::StructureFactory::StructureFactory( const char * field1, const char * field2, const char * field3, const char * field4 )
+{
+	std::list< const char * > fields;
+	fields.push_back( field1 );
+	fields.push_back( field2 );
+	fields.push_back( field3 );
+	fields.push_back( field4 );
+	init( fields );
+}
+
+void
+Kernel::StructureFactory::init( const std::list< const char * > & fields )
+{
+	Ast::ArgListExprs * tmp = new Ast::ArgListExprs( false );
+	typedef typeof fields ListType;
+	for( ListType::const_iterator i = fields.begin( ); i != fields.end( ); ++i )
+		{
+			(*tmp->namedExprs_)[ *i ] = 0;
+			typedef typeof values_ MapType;
+			values_.insert( MapType::value_type( *i, Kernel::THE_VOID_VARIABLE ) );
+		}
+	argList_ = tmp;
+}
+
+void
+Kernel::StructureFactory::clear( )
+{
+	typedef typeof values_ MapType;
+	for( MapType::iterator i = values_.begin( ); i != values_.end( ); ++i )
+		{
+			i->second = Kernel::THE_VOID_VARIABLE;
+		}
+}
+
+void
+Kernel::StructureFactory::set( const char * field, const Kernel::VariableHandle & value )
+{
+	typedef typeof values_ MapType;
+	MapType::iterator i = values_.find( field );
+	if( i == values_.end( ) )
+		{
+			throw Exceptions::InternalError( "Kernel::StructureFactory::set: Field was not declared." );
+		}
+	i->second = value;
+}
+
+RefCountPtr< const Lang::Structure >
+Kernel::StructureFactory::build( )
+{
+	RefCountPtr< const Lang::SingleList > tmp = Lang::THE_CONS_NULL;
+	typedef typeof values_ MapType;
+	for( MapType::iterator i = values_.begin( ); i != values_.end( ); ++i )
+		{
+			tmp = RefCountPtr< const Lang::SingleList >( new Lang::SingleListPair( i->second, tmp ) );
+		}
+	return RefCountPtr< const Lang::Structure >( new Lang::Structure( argList_, tmp ) );
+}
diff --git a/source/containertypes.h b/source/containertypes.h
index 49d6fbc4..aa46cbfc 100644
--- a/source/containertypes.h
+++ b/source/containertypes.h
@@ -156,6 +156,25 @@ namespace Shapes
 	};
 
 	}
+	namespace Kernel
+	{
+		class StructureFactory
+		{
+			const Ast::ArgListExprs * argList_;
+			std::map< const char *, Kernel::VariableHandle > values_;
+		private:
+			void init( const std::list< const char * > & fields );
+		public:
+			StructureFactory( const std::list< const char * > & fields );
+			StructureFactory( const char * field1 );
+			StructureFactory( const char * field1, const char * field2 );
+			StructureFactory( const char * field1, const char * field2, const char * field3 );
+			StructureFactory( const char * field1, const char * field2, const char * field3, const char * field4 );
+			void clear( );
+			void set( const char * field, const Kernel::VariableHandle & value );
+			RefCountPtr< const Lang::Structure > build( );
+		};
+	}
 }
 
 #endif
-- 
2.11.4.GIT