FnWrap2c - Configurabale binary argument wrapper template class
SYNOPSIS
#include <bobcat/fnwrap2c>
DESCRIPTION
The FBB::FnWrap2c class is a configurable binary argument context
wrapper template class. Its primary use is in combination with the generic
algorithms from the standard template libray. The called function expects a
local context struct which is used to pass arguments to the function
called by the generic algorithm which are available in the local context of
the called generic algorithm. The local context struct can be either a
const or non-const struct.
The callled function itself may be specified as one of the constructor's
arguments. It must be a (static member) function. Using a (static member)
function has various advantages, especially with the FnWrap?c classes to
which a local context can be passed:
There is no introduced uncertainty about the const-ness of the
callled function, as static member functions do not support
a const modifier;
The passed function can also be a free (global) function to which a
local context is passed;
The passed function can be a static member function of the class
using the generic algorithm to which the FBB::FnWrap2c object is passed. By
passing the calling object in the function's local context, the function may
directly access the calling object's members.
The passed function can be a static member function of the class
whose objects are passed to the function via the generic template function s
iterator parameters. In that case the function may directly access the passed
object's members.
Since no object is involved in calling the static function, no
ambiguity can arise as to whether an object reference or an object pointer
should be used in calling the function: static (member) functions may be
called without using objects.
The FBB::FnWrap2c template class has the following template parameters:
Type1: the type of the first argument passed to FBB::FnWrap2c's
operator()() function. Specify the type as the type of the first parameter
of the function whose address is passed to the constructor (i.e., specify a
plain value or a (const) pointer or reference).
Type2: the type of the second argument passed to FBB::FnWrap2c's
operator()() function. Specify the type as the type of the second parameter
of the function whose address is passed to the constructor.
Context: the local context struct. This struct is a local
struct, an object of which could have been defined immediatey before
applying the generic algorithm. The local context struct object may specify
values, references or pointers to entities that are available in the local
context where the generic algorithm is called.
If no generic algorithm would have been used, but a local implementation
of the generic algorithm would have been used instead, then the called
function would have received certain arguments. The local context struct is a
replacement of such a function's parameter list, mimicking the function's
parameter list in the struct definition. The function will now receive a
`standardized' parameter list, defined by the local context struct. The type
of the defined struct as specified in the parameterlist of the function
whose address is passed to FnWrap2c's constructor should be specified for
Context. E.g., LocalStruct &.
When a non-const reference or pointer is specified, the function may
modify the struct's value fields identically to the situation where the
field's values are passed to the function as reference parameters.
Local context structs may also be generated using the FBB::LC local
Context Struct generating template class. Using a template-generated local
context struct reduces namespace and class-pollution: the software engineer
does not have to put any effort in finding an appropriate struct name and
doesn't even have to enter the struct's definition in, e.g., a class
header. The template takes care of the definition an declaration of the proper
type which will thus be available to classes, member functions and free
functions. Cf. the lc(3bobcat) for details.
ReturnType: the ReturnType is by default defined as void. By
specifying another type, the FBB::FnWrap2c object's operator()()
function will return the called function's return value as a value of the
specified type. E.g, by specifying a boolReturnType, the
FBB::FnWrap2c object may be used as a Unary Predicate. Alternatively,
pointers or references may be specified as return values.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
This constructor expects two arguments: the address of a function to
call from within its operator()() member, and a local context struct
which is passed to the called function as its second argument.
When the function pointed to by fun is called from
FBB::FnWrap2c::operator()(), it receives the latter function's
arguments as its first two arguments and the local context struct as its third
argument. With (STL) generic algorithms, the template parameters Type1 and
Type2 must define the data type to which iterators eventually point.
Hint: In situations where no context other than the class Class to
which the class' (static) member function belongs must be used `Class
&obj' (or a (const) pointer) can be specified as the context parameter,
passing, e.g., *this as the context. The static member function may then
call any of the non-static member functions of the class Class using the
normal syntax (e.g., obj.member(argument) if the static function defines
as its second parameter Class &obj).
OVERLOADED OPERATOR
The following member function will call the function
that's passed to FBB::FnWrap2c's constructor. See the example below.
ReturnType operator()(Type1 param1, Type2 param2) const:
This function is called by generic algorithms, receiving the
dereferenced iterators that are managed by the generic algorithm as its
arguments (so, the iterators may point to modifiable Type1 and Type2
objects). This function calls the function specified at FBB::FnWrap2c's
constructor, passing its parameters to that function as its first
two arguments, and the local context as its third argument.
TYPEDEFS
The class defines three types, which are used by generic algorithms:
first_argument_type: , a synonym for the basic type specified with the
Type1 template parameter. E.g., if Type1 is specified as std::string
const * then argument_type will be std::string;
second_argument_type: , a synonym for the basic type specified with the
Type2 template parameter.
result_type: , a synonym for the basic type specified with the
ReturnType template parameter.
Caveat: the template parameter specifying the type of the local
context struct should probably not be specified as a value type as this will
result in copying the local context struct for each call of the FNWrap2c
object or of the function that it is provided with, making it impossible for
the algorithms to modify value- or pointer-fields of the outermost local
context struct. Instead, the template type specifying the type of the local
context struct should be specified as a pointer or reference template type
when instantiating the FnWrap1c object.
DISTRIBUTION FILES
bobcat_2.02.03-x.dsc: detached signature;
bobcat_2.02.03-x.tar.gz: source archive;
bobcat_2.02.03-x_i386.changes: change log;
libbobcat1_2.02.03-x_*.deb: debian package holding the
libraries;
libbobcat1-dev_2.02.03-x_*.deb: debian package holding the
libraries, headers and manual pages;
http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
COPYRIGHT
This is free software, distributed under the terms of the
GNU General Public License (GPL).