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# critcl::class(n) 1.1 doc "C Runtime In Tcl (CriTcl)"

## Name

critcl::class - CriTcl - Code Gen - C Classes

## Synopsis

- package require Tcl 8.6
- package require critcl ?3.2?
- package require critcl::class ?1.1?

- ::critcl::class::define name script
- include path
- support code
- type name
- classconstructor body
- classdestructor body
- constructor body ?postbody?
- destructor body
- classvariable ctype name ?comment? ?constructor? ?destructor?
- classmethod name command arguments body
- classmethod name proc arguments resulttype body
- classmethod name as funname ?arg...?
- insvariable ctype name ?comment? ?constructor? ?destructor?
- method name command arguments body
- method name proc arguments resulttype body
- method name as funname ?arg...?
- method_introspection

## Description

Be welcome to the C Runtime In Tcl (short: CriTcl), a system for embedding and using C code from within Tcl scripts.

This document is the reference manpage for the critcl::class package. This package provides convenience commands for advanced functionality built on top of the core.

With it a user wishing to create a C level object with class and instance commands can concentrate on specifying the class- and instance-variables and -methods in a manner similar to a TclOO class, while all the necessary boilerplate around it is managed by this package.

Its intended audience are mainly developers wishing to write Tcl packages with embedded C code.

This package resides in the Core Package Layer of CriTcl.

## API

::critcl::class::define name script

  This is the main command to define a new class name, where name is the name of the Tcl command representing the class, i.e. the class command. The script provides the specification of the class, i.e. information about included headers, class- and instance variables, class- and instance-methods, etc. See the section Class Specification API below for the detailed list of the available commands and their semantics.

## Class Specification API

Here we documents all class specification commands available inside of the class definition script argument of ::critcl::class::define.

### General configuration

include path

  This command specifies the path of a header file to include within the code generated for the class. This is separate from the support because the generated include directives will be put at the very beginning of the generated code. This is done to allow the use of the imported declarations within the instance type, and elsewhere.

  Calls to this command are cumulative. It is of course possible to not use this command at all, for classes not making use of external definitions.

  The result is the empty string.

support code

  This command specifies supporting C code, i.e. any definitions (types, functions, etc.) needed by the whole class and not fitting into class- and instance-methods. The code is embedded at global level, outside of any function or other definition.

  Calls to this command are cumulative. It is of course possible to not use this command at all, for classes not requiring supporting code.

  The result of the command is the empty string.

type name

  This command specifies the name of an external C type to be used as the type of the instance structure.

  Initialization and release of the structure with the given type are the responsibility of the user, through constructor and destructor code fragments.

  Attention: Using this command precludes the use of regular class- and instance variables. It further precludes the use of method-introspection as well, as this make use of generated instance-variables.

  If class- and/or instance-variable have to be used in conjunction with an external C type, simply create and use a class- or instance-variable with that type.

  The result of the command is the empty string.

### Class lifetime management

classconstructor body

  This command specifies a C code block surrounding the initialization of the class variables, i.e. the fields of the class structure. Note that allocation and release of the class structure itself is done by the system andf not the responsibility of the user.

  For the initialization (and release) of a class variable it is recommended to use the constructor and destructor arguments of the variable's definition (See command classvariable) for this instead of using a separate classconstructor.

  This is an optional command. Using it more than once is allowed too and each use will add another C code fragment to use during construction. I.e. multiple calls aggregate.

  The C code blocks of multiple calls (including the constructors of classvariable definitions) are executed in order of specification.

  The result of the command is the empty string.

  The C code in body has access to the following environment:

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the class structure will be associated with. It enables the generation of a Tcl error message should construction fail.

  class

    Pointer to the class structure to initialize.

  error

    A C code label the constructor can jump to should it have to signal a construction failure. It is the responsibility of the constructor to release any variables already initialized before jumping to this label. This also why the 'execution in order of specification' is documented and can be relied on. It gives us the knowledge which other constructors have already been run and initialized what other fields.

classdestructor body

  This command specifies a C code block surrounding the release of the class variables, i.e. the fields of the class structure. Note that allocation and release of the class structure itself is done by the system and not the responsibility of the user.

  For the initialization (and release) of a class variable it is recommended to use the constructor and destructor arguments of the variable's definition (See command classvariable) for this instead of using a separate classconstructor.

  This is an optional command. Using it more than once is allowed too and each use will add another C code fragment to use during construction. I.e. multiple calls aggregate.

  The C code blocks of multiple calls (including the constructors of class variable definitions) are executed in order of specification.

  The result of the command is the empty string.

  The C code in body has access to the same environment as the class constructor code blocks.

### Instance lifetime management

constructor body ?postbody?

  This command specifies a C code block surrounding the initialization of the instance variables, i.e. the fields of the instance structure. Note that allocation and release of the instance structure itself is done by the system and not the responsibility of the user. On the other hand, if an external type was specified for the instance structure, then instance variables are not possible, and the system has no knowledge of the type's structure. In that case it is the responsibility of the body to allocate and free the structure itself too.

  For the initialization (and release) of an instance variable it is recommended to use the constructor and destructor arguments of the variable's definition (See command insvariable) for this instead of using a separate constructor.

  This is an optional command. Using it more than once is allowed too and each use will add another C code fragment to use during construction. I.e. multiple calls aggregate.

  The C code blocks of multiple calls (including the constructors of instance variable definitions) are executed in order of specification.

  The result of the command is the empty string.

  The C code in body has access to the following environment:

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the instance structure will be associated with. It enables the generation of a Tcl error message should construction fail.

  instance

    Pointer to the instance structure to initialize.

  error

    A C code label the constructor can jump to should it have to signal a construction failure. It is the responsibility of the constructor to release any variables already initialized before jumping to this label. This also why the 'execution in order of specification' is documented and can be relied on. It gives us the knowledge which other constructors have already been run and initialized what other fields.

  The C code in postbody is responsible for construction actions to be done after the primary construction was done and the Tcl-level instance command was successfully created. It has access to a slightly different environment:

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the instance structure will be associated with. It enables the generation of a Tcl error message should construction fail.

  instance

    Pointer to the instance structure to initialize.

  cmd

    The Tcl_Command token of the Tcl-level instance command.

  fqn

    The fully qualified name of the instance command, stored in a Tcl_Obj*.

destructor body

  This command specifies a C code block surrounding the release of the instance variables, i.e. the fields of the instance structure. Note that allocation and release of the instance structure itself is done by the system and not the responsibility of the user. On the other hand, if an external type was specified for the instance structure, then instance variables are not possible, and the system has no knowledge of the type's structure. In that case it is the responsibility of the body to allocate and free the structure itself too.

  For the initialization (and release) of an instance variable it is recommended to use the constructor and destructor arguments of the variable's definition (See command insvariable) for this instead of using a separate constructor.

  This is an optional command. Using it more than once is allowed too and each use will add another C code fragment to use during construction. I.e. multiple calls aggregate.

  The C code blocks of multiple calls (including the constructors of instance variable definitions) are executed in order of specification.

  The result of the command is the empty string.

  The C code in body has access to the following environment:

  instance

    Pointer to the instance structure to release.

### Class variables and methods

classvariable ctype name ?comment? ?constructor? ?destructor?

  This command specifies a field in the class structure of the class. Multiple fields can be specified, and are saved in the order specified.

  Attention: Specification of a class variable precludes the use of an external C type for the instance structure.

  Attention: Specification of a class variable automatically causes the definition of an instance variable named class, pointing to the class structure.

  Beyond the basic name and C type of the new variable the definition may also contain a comment describing it, and C code blocks to initialize and release the variable. These are effectively local forms of the commands classconstructor and classdestructor. Please read their descriptions for details regarding the C environment available to the code.

  The comment, if specified will be embedded into the generated C code for easier cross-referencing from generated ".c" file to class specification.

classmethod name command arguments body

  This command specifies a class method and the C code block implementing its functionality. This is the first of three forms. The method is specified like a critcl::ccommand, with a fixed set of C-level arguments. The body has to perform everything (i.e. argument extraction, checking, result return, and of course the actual functionality) by itself.

  For this the body has access to

  class

    Pointer to the class structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the class structure is associated with

  objc

    The number of method arguments.

  objv

    The method arguments, as C array of Tcl_Obj pointers.

  The arguments of the definition are only a human readable form of the method arguments and syntax and are not used in the C code, except as comments put into the generated code. Again, it is the responsibility of the body to check the number of arguments, extract them, check their types, etc.

classmethod name proc arguments resulttype body

  This command specifies a class method and the C code block implementing its functionality. This is the second of three forms. The method is specified like a critcl::cproc. Contrary to the first variant here the arguments are computer readable, expected to be in the same format as the arguments of critcl::cproc. The same is true for the resulttype. The system automatically generates a wrapper doing argument checking and conversion, and result conversion, like for critcl::cproc.

  The body has access to

  class

    Pointer to the class structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the class structure is associated with

  ...

    All arguments under their specified names and C types as per their definition.

classmethod name as funname ?arg...?

  This command specifies a class method and the C code block implementing its functionality. This is the third and last of three forms.

  The class method is implemented by the external function funname, i.e. a function which is declared outside of the class code itself, or in a support block.

  It is assumed that the first four arguments of that function represent the parameters

  class

    Pointer to the class structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the class structure is associated with

  objc

    The number of method arguments.

  objv

    The method arguments, as C array of Tcl_Obj pointers.

  Any additional arguments specified will be added after these and are passed into the C code as is, i.e. are considered to be C expressions.

### Instance variables and methods

insvariable ctype name ?comment? ?constructor? ?destructor?

  This command specifies a field in the instance structure of the class. Multiple fields can be specified, and are saved in the order specified.

  Attention: Specification of an instance variable precludes the use of an external C type for the instance structure.

  Attention: Specification of an instance variable automatically causes the definition of an instance variable of type Tcl_Command, and named cmd, holding the token of the instance command, and the definition of an instance method named destroy. This implicit instance variable is managed by the system.

  Beyond the basic name and C type of the new variable the definition may also contain a comment describing it, and C code blocks to initialize and release the variable. These are effectively local forms of the commands constructor and destructor. Please read their descriptions for details regarding the C environment available to the code.

  The comment, if specified will be embedded into the generated C code for easier cross-referencing from generated ".c" file to class specification.

method name command arguments body

  This command specifies an instance method and the C code block implementing its functionality. This is the first of three forms. The method is specified like a critcl::ccommand, with a fixed set of C-level arguments. The body has to perform everything (i.e. argument extraction, checking, result return, and of course the actual functionality) by itself.

  For this the body has access to

  instance

    Pointer to the instance structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the instance structure is associated with

  objc

    The number of method arguments.

  objv

    The method arguments, as C array of Tcl_Obj pointers.

  The arguments of the definition are only a human readable form of the method arguments and syntax and are not used in the C code, except as comments put into the generated code. Again, it is the responsibility of the body to check the number of arguments, extract them, check their types, etc.

method name proc arguments resulttype body

  This command specifies an instance method and the C code block implementing its functionality. This is the second of three forms. The method is specified like a critcl::cproc. Contrary to the first variant here the arguments are computer readable, expected to be in the same format as the arguments of critcl::cproc. The same is true for the resulttype. The system automatically generates a wrapper doing argument checking and conversion, and result conversion, like for critcl::cproc.

  The body has access to

  instance

    Pointer to the instance structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the instance structure is associated with

  ...

    All arguments under their specified names and C types as per their definition.

method name as funname ?arg...?

  This command specifies an instance method and the C code block implementing its functionality. This is the third and last of three forms.

  The instance method is implemented by the external function funname, i.e. a function which is declared outside of the instance code itself, or in a support block.

  It is assumed that the first four arguments of that function represent the parameters

  instance

    Pointer to the instance structure.

  interp

    Pointer to the Tcl interpreter (Tcl_Interp*) the instance structure is associated with

  objc

    The number of method arguments.

  objv

    The method arguments, as C array of Tcl_Obj pointers.

  Any additional arguments specified will be added after these and are passed into the C code as is, i.e. are considered to be C expressions.

method_introspection

  This command generates one class- and one instance-method both of which will return a list of the instance methods of the class, and supporting structures, like the function to compute the information, and a class variable caching it.

  The two methods and the class variable are all named methods.

### Context dependent interactions

This section documents the various interactions between the specification commands. While these are are all documented with the individual commands here they are pulled together to see at a glance.

1. If you are using the command type to specify an external C type to use for the instance structure you are subject to the following constraints and rules:

   1. You cannot define your own instance variables.

   2. You cannot define your own class variables.

   3. You cannot use method_introspection.

   4. You have to allocate and release the instance structure on your own, through constructor and destructor code blocks.

2. If you declare class variables you are subject to the following constraints and rules:

   1. You cannot use type.

   2. The system generates an instance variable class for you, which points from instance to class structure. This makes you also subject to the rules below, for instance variables.

3. If you declare instance variables (possibly automatic, see above) you are subject to following constraints and rules:

   1. You cannot use type.

   2. The system generates and manages an instance variable cmd for you, which holds the Tcl_Command token of the instance command.

   3. The system generates an instance method destroy for you.

   4. The system manages allocation and release of the instance structure for you. You have to care only about the instance variables themselves.

## Example

The example shown below is the specification of queue data structure, with most of the method implementations and support code omitted to keep the size down.

The full implementation can be found in the directory "examples/queue" of the critcl source distribution/repository.

    package require Tcl 8.6
    package require critcl 3.2
    critcl::buildrequirement {
        package require critcl::class ; # DSL, easy spec of Tcl class/object commands.
    }
    critcl::cheaders util.h
    critcl::class::define ::queuec {
        include util.h
        insvariable Tcl_Obj* unget {
    	List object unget elements
        } {
    	instance->unget = Tcl_NewListObj (0,NULL);
    	Tcl_IncrRefCount (instance->unget);
        } {
    	Tcl_DecrRefCount (instance->unget);
        }
        insvariable Tcl_Obj* queue {
    	List object holding the main queue
        } {
    	instance->queue = Tcl_NewListObj (0,NULL);
    	Tcl_IncrRefCount (instance->queue);
        } {
    	Tcl_DecrRefCount (instance->queue);
        }
        insvariable Tcl_Obj* append {
    	List object holding new elements
        } {
    	instance->append = Tcl_NewListObj (0,NULL);
    	Tcl_IncrRefCount (instance->append);
        } {
    	Tcl_DecrRefCount (instance->append);
        }
        insvariable int at {
    	Index of next element to return from the main queue
        } {
    	instance->at = 0;
        }
        support {... queue_peekget, queue_size, etc.}
        method clear {} {...}
        method destroy {...}
        method get  as queue_peekget 1
        method peek as queue_peekget 0
        method put {item ...}
        method size {} {
    	if ((objc != 2)) {
    	    Tcl_WrongNumArgs (interp, 2, objv, NULL);
    	    return TCL_ERROR;
    	}
    	Tcl_SetObjResult (interp, Tcl_NewIntObj (queue_size (instance, NULL, NULL, NULL)));
    	return TCL_OK;
        }
        method unget {item} {...}
    }
    package provide queuec 1

## Authors

Andreas Kupries

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such at https://github.com/andreas-kupries/critcl. Please also report any ideas for enhancements you may have for either package and/or documentation.

## Keywords

C class, C code, C instance, C object, Embedded C Code, code generator, compile & run, compiler, dynamic code generation, dynamic compilation, generate package, linker, on demand compilation, on-the-fly compilation

## Category

Glueing/Embedded C code

## Copyright

Copyright © 2011-2018 Andreas Kupries