Re: Ada 2005?

[Martin Dowie <martin.dowie@btopenworld.com>]

conradwt@runbox.com wrote:
> Hi, will Ada support keyword class for designing and implementing
> classes?  For example, I'm forced to convert the following C++ class in
> Ada as follows:

Why are you hung up on having a keyword 'class'? 'Tagged types' in Ada 
do the same thing wrt dynamic dispatching and 'packages' give you 
namespaces/modules.


> // C++
> 
> class A_Device {
> 
> public:
> 
> A_Device( char*, int, int );

"char*" really ought to be a 'const'...


> char* Name( void );
> 
> int Major( void );
> 
> int Minor( void );

These really ought to be marked as 'const' functions...


> protected:
> 
> char* name;
> 
> int major;
> 
> int minor;
> };
> 
> // Now, if I need to interact with the, this class I can do the
> // following:
> 
> void main(void) {
> 
> A_Device aDevice = new A_Device( "Test", 1, 1 );
> 
> cout << aDevice.Name() << endl;
> cout << aDevice.Major() << endl;
> cout << aDevice.Minor() << endl;
> 
> }
> 
> // Ada
> 
> package Devices is
> 
> type Device is tagged private;
> 
> type Device_Type is access private;

You just don't need this access type



> function Create( Name : String,
> Major : Integer,
> Minor : Integer ) return Device_Type;

Just return something of type Device...


> function Name( this : Device_Type ) return String;
> 
> function Major( this : Device_Type ) return Integer;
> 
> function Minor( this : Device_Type ) return Integer;
> 
> private
> 
> type Device is tagged
> 
> record
> 
> name : String(1..20);
> major: Integer;
> minor: Integer;
> 
> end record;
> 
> end Devices;
> 
> Now, interact with Ada package I would need to do the following:
> 
> procedure main
> 
> aDevice : Device_Type := Devices.Create( "Test", 1, 1 );
> 
> begin
> 
> Put_Line( Name( aDevice ) );
> Put_Line( Major( aDevice ) );
> Put_line( Minor( aDevice ) );
> 
> end main;
> 
> It seems that I'm trying to mimic the behavior of a OO language in a
> procedural language when converting C++ to Ada.  Is this correct?  If
> so, why doesn't Ada have OO contructs similar to C++,
> Java, Eiffel, and Smalltalk to name a few where one passes a message to
> an instance of a class?  Will this be something in Ada 2005 because I
> have been able to find a good overview of the language to date?  Well,
> I must go and thanks for any comments that you may send me.

Ada does have OO behaviour - what isn't OO about the behaviour of a 
'tagged type'?

If you're bother that you can't say

"Put_Line (aDevice.Name);"

then wait for Ada200Y which adds this. But it is nothing more than 
playing with syntax - there is no symantic difference to this notation 
that to:

Put_Line (Name (aDevice));

Cheers

-- Martin