dtl

cb_ptr_fun() and cb_ptr_fun_w_ret()


Category: utilities	Component type: concept

Description

Use the cb_ptr_fun() and cb_ptr_fun_w_ret() template helper functions to wrap a raw function pointer or a pointer-to-member method into a function object. This mechanism allows you write regular C++ functions for use as a BCA , BPA, InsVal, SelVal, IOHandler, or SetParamsFn in an IndexedDBView. The single argument versions of cb_ptr_fun() and cb_ptr_fun_w_ret() accept a raw function pointer as their only argument while the two argument overloads also require an argument to the object to bind to the functor. Use cb_ptr_fun() for functions that do not return a value (return void) and cb_ptr_fun_w_ret() for functions that do return a value. You may wrap any C++ function that contains up to and including 4 arguments.

Definition

Defined in the variant_cc.h header file.

Refinement of

None.

Associated types

BPA, BCA, InsVal, SelVal, DBView, IndexedDBView, , IOHandler

Example 1:

//Simple use of cb_ptr_fun() with a BCA


// a BCA written as a simple function 
void BCAExample(BoundIOs &cols, Example &row)
{
  cols["INT_VALUE"]    == row.exampleInt;
  cols["STRING_VALUE"] == row.exampleStr;
  cols["DOUBLE_VALUE"] == row.exampleDouble;
  cols["EXAMPLE_LONG"] == row.exampleLong;
  cols["EXAMPLE_DATE"] == row.exampleDate;
}

// Read the contents of the DB_EXAMPLE table and return a vector of the
// resulting rows
vector<Example> ReadData()
{
 vector<Example> results;

 // the call to cb_ptr_fun() wraps BCAExample in a function object
 // so DTL may use it as the BCA for the DBView
 DBView<Example> view("DB_EXAMPLE", cb_ptr_fun(BCAExample));

 DBView<Example>::select_iterator read_it = view.begin();
 for ( ; read_it != view.end(); ++read_it)
 {
  results.push_back(*read_it);
 }

 return results;
}

Example 2:

//Simple use of cb_ptr_fun_w_ret() as a SelVal



// a typical SelVal function that we want to use in DTL
// an Example object is valid if all columns have a value
bool ExampleSelValidate(boundIOs &boundIOs, Example &rowbuf)
{
	for (BoundIOs::iterator b_it = boundIOs.begin();
				b_it != boundIOs.end(); b_it++)
	{
		BoundIO &boundIO = (*b_it).second;
		if (boundIO.IsColumn() && boundIO.IsNull())
			return false;  // found null column ... data is invalid
	}

	return true;	// no nulls found ... data is OK
}

// Read the contents of the DB_EXAMPLE table and return a vector of the
// resulting rows
vector<Example> ReadData()
{
 vector<Example> results;

 // the call to cb_ptr_fun_w_ret() wraps ExampleSelValidate in a function object
 // so DTL may use it as the SelVal for the DBView
 DBView<Example> view("DB_EXAMPLE", DefaultBCA<Example>(),
	"", DefaultBPA<Example>(), cb_ptr_fun_w_ret(ExampleSelValidate));

 DBView<Example>::select_iterator read_it = view.begin();
 for ( ; read_it != view.end(); ++read_it)
 {
  results.push_back(*read_it);
 }

 return results;
}

Notation:

`X`	A type that is a model of BoundIO
`a`	Object of type `X`

Expression semantics

Name	Expression	Semantics
Wrap function ptr. for functions returning void	cb_ptr_fun(func_ptr)	Wraps the raw function pointer func_ptr into a function object in the CBFunctor family. See Note [1].
Wrap function ptr. for functions returning a value	cb_ptr_fun_w_ret(func_ptr)	Wraps the raw function pointer func_ptr into a function object in the CBFunctor family.See Note [1].
Wrap pointer-to-member methods returning void	cb_ptr_fun(obj, ptr_to_member)	Wraps the pointer-to-member method into a function object in the CBFunctor family.See Note [1]. The type of the bound object does not figure in the signature of the functor ... only the method arguments and return type matter.
Wrap pointer-to-member methods returning a value	cb_ptr_fun_w_ret(obj, ptr_to_member)	Wraps the pointer-to-member method into a function object in the CBFunctor family.See Note [1]. The type of the bound object does not figure in the signature of the functor ... only the method arguments and return type matter.

Notes

[1] The CBFunctor family of functions is defined in the C++ Callback Library created by Rich Hickey. For information, go to http://www.bestweb.net/~rhickey/. Much of the DTL implementation uses a modified and extended form of this library wherever function objects are required.