DEV-10: Object-oriented Language Constructs for the 4GL

DEV-10:Object-oriented Language Constructs for the 4GL

Evan BleicherDevelopment Manager

2 DEV-10, Object-oriented 4GL Constructs© 2005 Progress Software Corporation

D I S C L A I M E R

Under Development

This talk includes information about potential future products and/or product enhancements.

What I am going to say reflects our current thinking, but the information contained herein is preliminary and subject to change. Any future products we ultimately deliver may be materially different from what is described here.

D I S C L A I M E R


Agenda

OO Overview Anatomy of a

CLASS Objects Inheritance Compiler changes Interoperability


Object-Oriented Overview

Class – Data members and methods

Object – Runtime instance of a class

Object Reference

– Strongly typed object handle

Typing – Type consistency enforced

Interface – Set of method definitions


Object-Oriented OverviewClass: Order

PRIVATE:

orderNum AS INT

CalculatePrice ( )

PROTECTED:

CalculateTax ( )

PUBLIC:

CreateOrder ( )

GetOrderTotal ( )

Inheritance – Reuse and specialize

code

Super Class – Common features

inherited by another class

Subclass – Inherits features from

another class

Override – Derived class

customized behavior

Class: InternalOrder

PUBLIC:

GetOrderTotal ( )


Benefits of OO in the 4GL

Programming Business

1. Productivity2. Easy to develop 3. Maintenance4. Robustness5. Ease of use

1. Code Reuse2. Inheritance 3. Encapsulation4. Strong typing5. Invocation

model


Similarities betweenClasses and Procedures

Classes Procedures

1. Procedure file2. Define variables3. Internal procedures4. User defined functions5. Code in main block6. Super procedures

1. Class files2. Data members3. VOID methods4. Other methods5. Constructor6. Inheritance


Agenda




Anatomy of a Class

CLASS <class-type>

[options]:

[ <data member> …]

[ <constructor> ]

[ <method> … ]

[ <destructor> ]

END [ CLASS ].


acme\request\Order.cls

CLASS acme.request.Order:

CLASSStatement

CLASS <class-type>

[ INHERITS <super-class-type> ]

[ IMPLEMENTS <interface-type>

[, <interface-type> ]… ]

[ FINAL ]:

[package.]classname

ProPath

\acme

\request

\Order.cls

\Order.r



END CLASS.

Example:Defining a CLASS hierarchy


CLASS acme.request.InternalOrder

INHERITS acme.request.Order:

END CLASS.

acme\request\InternalOrder.cls


Data Members

New keyword added to existing DEFINE syntax– PRIVATE (default)

– PROTECTED

– PUBLIC Defined outside of methods Scoped to class Define state an object


Example:Defining Data Members



DEFINE PUBLIC VARIABLE ShipDate AS DATE.

DEFINE PROTECTED TEMP-TABLE SalesRepTT

FIELD RepName AS CHAR

FIELD Region AS CHAR.

DEFINE PRIVATE VARIABLE OrderNum AS INT.

END CLASS.


Anatomy of a Method

METHOD [PRIVATE | PUBLIC | PROTECTED ]

[ FINAL]

{ VOID | <return-type> }

<method-name>

( [ <parameter> [ ,<parameter> ]… ] ):

<method-body>

END [METHOD].



DEFINE PRIVATE VARIABLE OrderNum AS INTEGER.

METHOD PUBLIC INTEGER GetOrderNum ( ):

RETURN OrderNum.

END METHOD.

END CLASS.

Example:Defining Methods




DEFINE PRIVATE VARIABLE OrderNum AS INTEGER.

METHOD PUBLIC VOID SetOrderNum

(INPUT ordNum AS INTEGER ):

OrderNum = ordNum.

END METHOD.

END CLASS.

Example:Defining Methods



Anatomy of a Constructor

CONSTRUCTOR [ PUBLIC | PROTECTED]

<class-name>

( [ <parameter> [ ,<parameter> ]… ] ):

<constructor-body>

END [CONSTRUCTOR].



CONSTRUCTOR PUBLIC Order ( ) :

/* Initialize data members */

END CONSTRUCTOR.

END CLASS.

Example:Defining Constructor



Anatomy of a Destructor

DESTRUCTOR [ PRIVATE ]

<class-name> ( ):

<destructor-body>

END [DESTRUCTOR].



DESTRUCTOR PRIVATE Order ( ) :

/* Perform cleanup of resources. */

END DESTRUCTOR.

END CLASS.

Example:Defining Destructor



Anatomy of an Interface

INTERFACE <interface-type>:

[ <temp-table> | <ProDataSet> ]

[ <method> …]

END [INTERFACE].


INTERFACE acme.navigation.support.IList:

METHOD PUBLIC VOID Next ( ).

METHOD PUBLIC VOID Prev ( ).

METHOD PUBLIC VOID First ( ).

METHOD PUBLIC VOID Last ( ).

END INTERFACE.

Example:Defining an Interface

acme\navigation\support\IList.cls


CLASS acme.request.InternalOrder

INHERITS acme.request.Order

IMPLEMENTS acme.navigation.support.IList:

METHOD PUBLIC VOID Next ( ) :/* Implementation of Next Method */

END METHOD.

/* Repeat for Prev, First and Last … */

END CLASS.

Example:Implementing an Interface



Agenda




Instantiating an object

NEW statement

Creates an instance of the class

Strongly typed object reference

Causes constructor to be invoked– Execution of all constructors in hierarchy

chain


NEW Statement

DEFINE VARIABLE <object-ref > AS

[ CLASS ] <class-type>.

<object-ref > = NEW <class-type >

( <parameter> [ ,<parameter> ]… )

[ ON <server-handle> ] [ NO-ERROR ].


DEFINE VARIABLE rIntOrderObj AS

CLASS acme.request.InternalOrder.

rIntOrderObj =

NEW acme.request.InternalOrder ( ).

Example:Instantiating an Object


Accessing Data Members & Methods

An Object Reference can access– PUBLIC Data Members

– PUBLIC Methods

– rIntOrderObj:shipDate

– rIntOrderObj:GetOrderNum ( )


Accessing Data Members & Methods

Within a class hierarchy– PUBLIC or PROTECTED Data Members– PUBLIC or PROTECTED Methods– SalesRepTT.RepName– protectedMethod ( )

Within a class– PRIVATE Data Members – PRIVATE Methods– orderNum– CalculatePrice ( )


Agenda




Inheritance

Subclass inherits super class’– PUBLIC & PROTECTED data members– PUBLIC & PROTECTED methods

Subclass can:– add additional capabilities– augment behavior of super class– override behavior of super class


InternalOrder

Overriding

Order

METHOD VOID GetOrderTotal ( ):

SUPER-CLASS:GetOrderTotal ( ).

END METHOD.

METHOD VOID GetOrderTotal ( ):

END METHOD.

Overridden method must have same signature

To access any super class’ method use SUPER-CLASS:

<method-name>

Always invoke method in most-derived object!


METHOD PUBLIC DECIMAL GetOrderTotal ( ):

/* Calculate total */

RETURN totalOrder.

END METHOD.

Example:Overriding


METHOD PUBLIC DECIMAL GetOrderTotal ( ):

DEFINE VAR dTotal AS DECIMAL.

dTotal = SUPER-CLASS:GetOrderTotal ( ).

RETURN dTotal * dDiscount.

END METHOD.



InternalOrder

DEFINE VAR rIntOrderObj AS

acme.request.InternalOrder.

rIntOrderObj = NEW

acme.request.InternalOrder ( ).

rIntOrderObj:GetOrderTotal ( ).

Example:Calling Overridden Method

Order

GetOrderTotal:

RETURN SUPER-CLASS:

GetOrderTotal ( ) * discount.

GetOrderTotal:

RETURN total.


Agenda




Compiler changes

Two – pass compiler Compile time validation of object

reference Validates

– Methods

– Parameters Compiles all files in class hierarchy


Agenda




InteroperabilityProcedures and Classes

Procedures – Can NEW a CLASS

– Can DELETE an object

– Invoke methods using object reference

– Can pass object reference as a parameter

Classes– Can RUN a procedure

– Can invoke internal procedure / udf using procedure handle


Integration with tools

New IDE

Procedure Editor

Procedure Window

Debugger


Future

Phased approach

Overloading

Arrays of object references

Available via Open Client

Improved Error Handling


In Summary

Standard OO concepts available in the 4GL

Built on top of existing 4GL constructs

Interoperability with Procedure / Functions


Questions?


Thank you for your time!


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DEV-10: Object-oriented Language Constructs for the 4GL

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