Copyright (c) 2002
Kevin Atkinson
kevina@gnu.org
This manual is designed for those who which to developer Aspell. It is currently very sketchy. However, it should improve over time. The latest version of this document can be found at http://savannah.gnu.org/download/aspell/manual/devel/devel.html.
The eventual goal is to convert this manual into Texinfo. However, since I do not have the time to learn Texinfo right now, I decided to use something I am already conferable with. Once someone goes through the trouble of converting it into Texinfo I will maintain the Texinfo version.
Copyright (c) 2002 Kevin Atkinson. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts. and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
As far as coding styles go I am really not that picky. The important thing is to stay consistent. However, please what ever you do, do not indent with more than 4 characters as I find indenting with more than that extremely difficult to read as most of the code ends up on the right side of the window.
The C++ Standard library is not used directly except under very specific circumstances. The string class and the STL is used indirectly though wrapper classes and all I/O is done using the standard C library with light right helper classes to make using C I/O a bit more C++ like.
However the new, new[], delete and delete[] operates are used to allocated memory when appropriate.
Templates are used in Aspell when there is a clear advantage to doing so. When ever you use templates please use them carefully and try very hard not to create code bloat by generating a lot of unnecessary, and duplicate code.
Exceptions are not used in Aspell as I find them more trouble than they are worth. Instead an alternate method of error handling is used which is based around the PosibErr class. PosibErr is a special Error handling device that will make sure that an error is properly handled. It is defined in ``posib_err.hpp''. PosibErr is expected to be used as the return type of the function It will automatically convert to the "normal" return type however if the normal returned type is accessed and there is an "unhandled" error condition it will abort It will also abort if the object is destroyed with an "unhandled" error condition. This includes ignoring the return type of a function returning an error condition. An error condition is handled by simply checking for the presence of an error, calling ignore, or taking ownership of the error.
The PosibErr class is used extensively though out Aspell. Please refer to the Aspell source for examples of using PosibErr until better documentation is written.
The String class provided the same functionally of the C++ string except for fewer constructors. It also inherits OStream so that you can write to it with the ``<<'' operator. It is defined in ``string.hpp''.
ParmString is a special string class that is designed to be used as a parameter for a function that is expecting a string. It is defined in ``parm_sting.hpp''. It will allow either a "const char *" or "String" class to be passed in. It will automatically convert to a "const char *". The string can also be accesses via the "str" method. Usage example:
A character vector is basically a Vector<char> but it has a few additional methods for dealing with strings which Vector does not provide. It, like String, is also inherits OStream so that you can write to it with the ``<<'' operator. It is defined in ``char_vector.hpp''. Use it when ever you need a string which is guaranteed to be in a continuous block of memory which you can write to.
Smart pointers are used extensively in Aspell to avoid simplify memory management tasks and to avoid memory leaks.
The CopyPtr class makes a deep copy of an object when ever it is copied. The CopyPtr class is defined in ``copy_ptr.hpp''. This header should be included where ever CopyPtr is used. The complete definition of the object CopyPtr is pointing to does not need to be defined at this point. The implementation is defined in ``copy_ptr-t.hpp''. The implementation header file should be included at a point in your code where the class CopyPtr is pointing to is completely defined.
ClonePtr is like copy pointer except the clone() method is used instead of the copy constructor to make copies of an object. If is defined in ``clone_ptr.hpp'' and implemented in ``clone_ptr-t.hpp''.
A StackPtr is designed to be used when ever the only pointer to a new object allocated with new is on the stack. It is similar to the standard C++ auto_ptr but the semantics are a bit different. It is defined in ``stack_ptr.hpp'' unlike CopyPtr of ClonePtr it is defined and implemented in this header file.
A generalized version of CopyPtr and ClonePtr which the two are based on. It is defined in ``generic_copy_ptr.hpp'' and implemented in ``generic_copy_ptr-t.hpp''.
Aspell does not use C++ I/O classes and function in any way since they do not provide a way to get at the underlying file number and can often be slower than the highly tuned C I/O functions found in the standard C library. However, some light weight wrapper classes are provided so that standard C I/O can be used in a more C++ like way.
These two base classes mimic some of the functionally of the C++ functionally of the corresponding classes. They are defined in ``istream.hpp'' and ``ostream.hpp'' respectfully. They are however based on standard C I/O and are not proper C++ streams.
Defined in ``fstream.hpp''
CIN/COUT/CERR. Defined in ``iostream.hpp''.
The Config class is used to hold configuration information. It has a set of keys which it will except. Inserting or even trying to look at a key that it does not know will produce an error. It is defined in ``common/config.hpp''
In Aspell there are 5 types of filters:
To add a new filter create a new file in the modules/filter directory, the file should be a C++ file and end in ``.cpp''. The file should contain a new filter class inherited from IndividualFilter, a function to return a new filter, and an optional KeyInfo array for adding options to control the behavior of the filter. The file then needs to be added to Makefile.am so that the build system knows about the filter and lib/new_filter.cpp must be modified so that Aspell knows about the filter.
All filters are required to inherit from the IndividualFilter class found in ``indiv_filter.hpp''. See that file for more details and the other filter modules for examples of how it is used.
After the class is created a function must to created which will return a new filter allocated with new. The function must have the following prototype:
A filter group may have any number of options associated with it as long as they all start with the filter name. See the TEX and SGML filter for examples of what to do and ``config.hpp'' for the definition of the KeyInfo struct.
After the new file is created simply add the file to the ``libaspell_filter_standard_la_SOURCES'' line in ``modules/filter/Makefile.am'' so that the build system knows about it.
Finally modify ``lib/new_filter.cpp'' so that Aspell knows about the new filter. Follow the example there for the other filter modules. The filter_modules array should only be modified if there your filter has config options.
When ever possible you should try to use on of the data structures available. If the data structures do not provide enough functionally for your needs you should consider enhancing them rather than written something from scratch.
The vector class is defined in ``vector.hpp'' and works the same way as the standard STL vector does except that it doesn't have as many constructors.
BasicList is a simple list structure which can either be implemented as a singly or doubly linked list. It is defined in ``basic_list.hpp''.
StringMap is a associative array for strings. You should try to use this when ever possible to avoid code bloat. It is defined in ``string_map.hpp''
Several hash tables are provided when StringMap is not appropriate. These hash tables provide a hash_set, hash_multiset, hash_map and hash_multimap which are very similar to SGI STL's implementation with a few exceptions. It is defined in ``hash.hpp''
BlockSList provided a pool of nodes which can be used for singly linked lists. It is defined in ``block_slist.hpp''.
A good deal of interface code is automatically generated by the ``mk-src.pl'' Perl script. I am doing it this way to avoid having to write a lot of relative code for the C++ interface. This should also make adding interface for other languages a lot less tedious and will allow the interface to automatically take advantage of new Aspell functionality as it is made available. The ``mk-src.pl'' script uses ``mk-src.in'' as its input.
The format of mk-src.in is as follows:
The following charaters are literals: { } / '\ ' \n = >
<items>
<items> := (<item>\n)+
<items> := <category>:\ <name> {\n<details>\n} | <<tab>><details>
<details> := <options>\n /\n <items>
<options> := (<option>\n)*
<option> := <key> [=> <value>]
<<tab>> means everything should be indented by one tab
See MkSrc::Info for a description of the categorys and options
The info array contains information on how to process the info in mk-src.pl. It has the following layout
<catagory> => options => []
groups => [] # if undef than anything is accepted
creates_type => "" # the object will create a new type
# as specified
proc => <impl type> => sub {}
where <impl type> is one of:
cc: for "aspell.h" header file
cxx: for C++ interface implemented on top of cc interface
native: for creation of header files used internally by aspell
impl: for defination of functions declared in cc interface.
the definations use the native hedaer files
native_impl: for implementations of stuff declared in the native
header files
each proc sub should take the following argv
$data: a subtree of $master_data $accum:
<options> is one of:
desc: description of the object
prefix:
posib err: the method may return an error condition
c func:
const: the method is a const member
c only: only include in the external interface
c impl headers: extra headers that need to be included in the C impl
c impl: use this as the c impl instead of the default
cxx impl: use this as the cxx impl instead of the default
returns alt type: the constructor returns some type other than
the object from which it is a member of
no native: do not attemt to create a native implementation
treat as object: treat as a object rather than a pointer
The %info structure is initialized as follows:
our %info =
(
root => {
options => [],
groups => ['methods', 'group']},
methods => {
# methods is a collection of methods which will be inserted into
# a class after some simple substation rules. A $ will be
# replaced with name of the class.
options => ['strip', 'prefix', 'c impl headers'],
groups => undef},
group => {
# a group is a colection of objects which should be grouped together
# this generally means they will be in the same source file
options => ['no native'],
groups => ['enum', 'struct', 'union', 'func', 'class', 'errors']},
enum => {
# basic C enum
options => ['desc', 'prefix'],
creates_type => 'enum'},
struct => {
# basic c struct
options => ['desc', 'treat as object'],
groups => undef,
creates_type => 'struct',},
union => {
# basic C union
options => ['desc', 'treat as object'],
groups => undef,
creates_type => 'union'},
class => {
# C++ class
options => ['c impl headers'],
groups => undef,
creates_type => 'class'},
errors => {}, # possible errors
method => {
# A class method
options => ['desc', 'posib err', 'c func', 'const',
'c only', 'c impl', 'cxx impl'],
groups => undef},
constructor => {
# A class constructor
options => ['returns alt type', 'c impl', 'desc'],
groups => 'types'},
destructor => {
# A class destructor
options => [],
groups => undef},
);
In addition to the categories listed above a "methods" catagory by be specified in under the class category. A "methods" catagory is created for each methods group under the name "<methods name> methods" When groups is undefined a type name may be specified in place of a category
types contains a master list of all types. This includes basic types and ones created in mk-src.in. The basic types include:
'void', 'bool', 'pointer', 'double',
'string', 'encoded string', 'string obj',
'char', 'unsigned char',
'short', 'unsigned short',
'int', 'unsigned int',
'long', 'unsigned long'
%methods is used for holding the "methods" information
This module contains various useful utility functions:
Returns 0.
Returns 1.
Apply EXPR to each item in LIST and than concatenate the result into a string
Returns true if LIST contains at least one of STR.
Convert STR to all uppercase and substitute spaces with underscores.
Convert STR to all lowercase and substitute spaces with underscores.
Convert STR to mixed case where each new word startes with a uppercase letter. For example "feed me" would become "FeedMe".
Read in "mk-src.in" and returns a data structure which has the following format:
<tree>
<tree> := <options>
data => <tree>
where each tree represents an entry in mk-src.in.
The following two options are always provided:
name: the name of the entry
type: the catagory or type name
Additional options are the same as specified in %info
Create a source file.
Required Parms: type, dir, name, data Boolean Parms: header, cxx Optional Parms: namespace (required if cxx), pre_ext, accum
Writes DATA to FILENAME but only if DATA differs from the content of the file and the string:
Automatically generated file.
is present in the existing file if it already exists.
The code generation modes are currently one of the following:
cc: Mode used to create types suitable for C interface cc_cxx: Like cc but typenames don't have a leading Aspell prefix cxx: Mode used to create types suitable for CXX interface native: Mode in which types are suitable for the internal implementation native_no_err: Like Native but with out PosibErr return types
Helper functions used by interface generation code:
.
.
Creates a function prototype
Parms can be any of:
mode: code generation mode
Return a string to call a func. Will prefix the function with return if the functions returns a non-void type;
Parms can be any of:
mode: code generation mode
Converts item into a type name.
Parms can be any of:
mode: code generation mode use_type: include the actual type use_name: include the name on the type pos: either "return" or "other"
Make a C comment out of DESC optionally indenting it LEVEL spaces.
Create the phototype for a C method which is really a function.
Parms is any of:
mode: code generation mode no_aspell: if true do not include aspell in the name this_name: name for the paramater representing the current object
Like make_c_method but instead returns the appropriate string to call the function. If the function returns a non-void type the string will be prefixed with a return statement.
Like make_c_method except that it returns the array:
($func, $data, $parms, $accum)
which is suitable for passing into make_func. It will return an empty array if it can not make a method from ITEM.
Create the phototype for a C++ method.
Parms is one of:
mode: code generation mode
Version 1.1, March 2000
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