Hi

I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.

I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.

I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.

I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:

$selected = 1;
$classes = array('class1','class2');
$className = $classes[$selected];
$object = new $className;

Thanks for any help.

Thomas

Thomas wrote:
> Hi
> 
> I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.
> 
> I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.
> 
> I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
> 
> I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:
> 
> $selected = 1;
> $classes = array('class1','class2');
> $className = $classes[$selected];
> $object = new $className;
> 
> Thanks for any help.
> 

This can't really be done in D, which is statically typed. Languages like PHP are dynamically typed. You'll have to do some re-thinking of your design, I think.

First, you'll want all of your classes to either derive from the same class or implement the same interface. Let's call this base class (or interface) Base.

You could try something like this:

int selected = 1;
Base object;

switch (selected) {
    case 1:
        object = new Class1;
        break;
    case 2:
        object = new Class2;
        break;
    // and so on
}

You might also consider using an enum instead of an int for selected.

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://pyd.dsource.org

Kirk McDonald Wrote:

> Thomas wrote:
> > 
> > I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
> > 
> This can't really be done in D, which is statically typed. Languages like PHP are dynamically typed. You'll have to do some re-thinking of your design, I think.

Thanks a lot. I will exercise a little more with that information.

Hi Thomas,

'The other' Thomas (Khuene) has created a lib, Flectioned, that can do just that. IRC, it only works for linux.

http://flectioned.kuehne.cn

L.

On 2007-01-27 19:30:04 -0800, Thomas <thc@forestfactory.de> said:

> Hi
> 
> I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.
> 
> I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.
> 
> I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
> 
> I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:
> 
> $selected = 1;
> $classes = array('class1','class2');
> $className = $classes[$selected];
> $object = new $className;
> 
> Thanks for any help.
> 
> Thomas

I'm not sure what you'd be doing where this would be an optimal solution, but you can do something like this:

ushort selected = 1;
Object[] classes = [new Class1, new Class2];
Object foo = classes[selected].dup;

I believe....

Thomas wrote:
> Hi
> 
> I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.
> 
> I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.
> 
> I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
> 
> I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:
> 
> $selected = 1;
> $classes = array('class1','class2');
> $className = $classes[$selected];
> $object = new $className;
> 
> Thanks for any help.
> 
> Thomas

(This probably goes in D.learn by the way.)

If you have a class that follows a common interface (I'll call it Command) you could do this:

class Command {
    static Command[char[]] actions;

    this(char[] name)
    {
         actions[name] = this;
    }

    static void run(char[] name, char[] arguments)
    {
        assert(name in actions);
        actions[name].work(arguments);
    }

    abstract void work(char[] arguments);
};

Then you can create instance of Command:

class Rename : Command {
    this()
    {
        super("rename");
    }

    void work(char[] arguments)
    {
        // do a rename or something
    }
};

If you create one object of each subclass:

Rename r = new Rename;

The calling code could do this:

Command.run("rename", "a b");

Which would run the Rename.work() command.

Kevin

Kevin Bealer wrote:
> Thomas wrote:
>> Hi
>>
>> I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.
>>
>> I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.
>>
>> I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
>>
>> I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:
>>
>> $selected = 1;
>> $classes = array('class1','class2');
>> $className = $classes[$selected];
>> $object = new $className;
>>
>> Thanks for any help.
>>
>> Thomas
> 
> (This probably goes in D.learn by the way.)
> 
> If you have a class that follows a common interface (I'll call it Command) you could do this:
> 
> class Command {
>     static Command[char[]] actions;
> 
>     this(char[] name)
>     {
>          actions[name] = this;
>     }
> 
>     static void run(char[] name, char[] arguments)
>     {
>         assert(name in actions);
>         actions[name].work(arguments);
>     }
> 
>     abstract void work(char[] arguments);
> };
> 
> Then you can create instance of Command:
> 
> class Rename : Command {
>     this()
>     {
>         super("rename");
>     }
> 
>     void work(char[] arguments)
>     {
>         // do a rename or something
>     }
> };
> 
> If you create one object of each subclass:
> 
> Rename r = new Rename;
> 
> The calling code could do this:
> 
> Command.run("rename", "a b");
> 
> Which would run the Rename.work() command.
> 
> Kevin

Wow, that is an effective solution, never seen that pattern before.

Thomas wrote:
> Hi
> 
> I'm just making my first steps to understand D, and sometimes I'm a little bit offroad as I do not know C/C++, just PHP, Javascript etc.
> 
> I would like to write a small shell application with a small bundle of functionalities. As a first step, the user must choose which function to use (I already got that part). Than she must enter some information for the function to work on.
> 
> I thought of doing this by creating classes for each functionality implementing the same interface and creating an array in main() that somehow refers to these classes. There the trouble starts.
> 
> I don't know how to create such an array, and of which type it has to be. To be more specific, I provide you with a PHP example of what I want to do:
> 
> $selected = 1;
> $classes = array('class1','class2');
> $className = $classes[$selected];
> $object = new $className;
> 
> Thanks for any help.
> 
> Thomas

Thomas wrote:
> $selected = 1;
> $classes = array('class1','class2');
> $className = $classes[$selected];
> $object = new $className;
> 
> Thanks for any help.
> 
> Thomas


This version is very similar an more efficient though the array initialization is more verbose.

Kirk McDonald wrote:
> This can't really be done in D, which is statically typed. Languages like PHP are dynamically typed. You'll have to do some re-thinking of your design, I think.

Well, Java is statically typed, and it can do what the OP requested.

It's not really a question of dynamic/static typing. It's more a question of whether runtime reflection is supported. And right now, D's runtime reflection capabilities aren't as complete as Java's.

Personally, I'm not crazy about reflection-heavy code, since I think it provides a sneaky mechanism for subverting the compile-time type-checking system. Debugging Java code that makes heavy use of reflection is not a pleasant experience (since all of your exceptions get swallowed up in the reflection API, as InvocationTargetExceptions).

--benji