Suppose I have a base class with many ctors().

I want to inherit from the base class and make one slight alteration to it, but I don't want to write X times the following:

this(args) {
  super(args);
}

Does D have an easy way for the derived class to 'inherit' all or some of the
base class ctors(), and just override/add ctors() in the derived class?

In Java, we can use eclipse to auto-generate code for us.  :)  But, the results look cluttered, and it's really not a solution.

Anyways, just curious.

thanks.

On Thu, 05 Aug 2010 13:53:20 -0400, dcoder <dcoder@devnull.com> wrote:

> Suppose I have a base class with many ctors().
>
> I want to inherit from the base class and make one slight alteration to it,
> but I don't want to write X times the following:
>
> this(args) {
>   super(args);
> }
>
> Does D have an easy way for the derived class to 'inherit' all or some of the
> base class ctors(), and just override/add ctors() in the derived class?

Sadly, no.  It's been discussed in the past.  I was surprised there were no enhancement requests for it in bugzilla, care to add one?

You may be able to do it with templated constructors, but documentation would suck...

-Steve

dcoder <dcoder@devnull.com> wrote:

> Suppose I have a base class with many ctors().
>
> I want to inherit from the base class and make one slight alteration to it,
> but I don't want to write X times the following:
>
> this(args) {
>   super(args);
> }
>
> Does D have an easy way for the derived class to 'inherit' all or some of the
> base class ctors(), and just override/add ctors() in the derived class?

No easy way, no. The best solution might be template or string mixins.

-- 
Simen

Steven Schveighoffer Wrote:

> On Thu, 05 Aug 2010 13:53:20 -0400, dcoder <dcoder@devnull.com> wrote:
> 
> > Suppose I have a base class with many ctors().
> >
> > I want to inherit from the base class and make one slight alteration to
> > it,
> > but I don't want to write X times the following:
> >
> > this(args) {
> >   super(args);
> > }
> >
> > Does D have an easy way for the derived class to 'inherit' all or some
> > of the
> > base class ctors(), and just override/add ctors() in the derived class?
> 
> Sadly, no.  It's been discussed in the past.  I was surprised there were no enhancement requests for it in bugzilla, care to add one?

If it helps, I wrote up something on this a few years back:

http://www.digitalmars.com/d/archives/digitalmars/D/Inheriting_constructors_54088.html

Might be a good starting point for an enhancement request.

Sean Kelly wrote:

> Steven Schveighoffer Wrote:
> 
>> On Thu, 05 Aug 2010 13:53:20 -0400, dcoder <dcoder@devnull.com> wrote:
>> 
>> > Suppose I have a base class with many ctors().
>> >
>> > I want to inherit from the base class and make one slight alteration to
>> > it,
>> > but I don't want to write X times the following:
>> >
>> > this(args) {
>> >   super(args);
>> > }
>> >
>> > Does D have an easy way for the derived class to 'inherit' all or some
>> > of the
>> > base class ctors(), and just override/add ctors() in the derived class?
>> 
>> Sadly, no.  It's been discussed in the past.  I was surprised there were no enhancement requests for it in bugzilla, care to add one?
> 
> If it helps, I wrote up something on this a few years back:
> 
> 
http://www.digitalmars.com/d/archives/digitalmars/D/Inheriting_constructors_54088.html
> 
> Might be a good starting point for an enhancement request.


I've been trying to make a template for this but it seems that dmd still won't allow me to get the parameters of the constructors. dmd Seems to think that I'm trying to use it as a property.

Using getOverloads, one should be able to generate or select any of super's constructors. No need for enhancement, just a bug fix. see below:

import std.traits;
import std.conv;


class A {
    int i;
    this(int x) {
        i = x;
    }
    this(float x) {
        i = cast(int)x; // ignore bad code
    }
    this(string s) {
        i = to!int(s);
    }
}
void main() {
    foreach (m; __traits(getOverloads, A, "__ctor")) {
        pragma(msg, m.stringof); // it thinks I'm calling m
    }
}

constructors.d(34): Error: constructor constructors.A.this (int x) is not
callable using argument types ()
constructors.d(34): Error: expected 1 function arguments, not 0
this()
constructors.d(34): Error: constructor constructors.A.this (float x) is not
callable using argument types ()
constructors.d(34): Error: expected 1 function arguments, not 0
this()
constructors.d(34): Error: constructor constructors.A.this (string s) is not
callable using argument types ()
constructors.d(34): Error: expected 1 function arguments, not 0
this()

On Fri, Aug 6, 2010 at 11:43, Rory Mcguire <rjmcguire@gm_no_ail.com> wrote:


> I've been trying to make a template for this but it seems that dmd still
> won't allow me to get the parameters of the constructors. dmd Seems to
> think
> that I'm trying to use it as a property.
>
>

> void main() {
>    foreach (m; __traits(getOverloads, A, "__ctor")) {
>        pragma(msg, m.stringof); // it thinks I'm calling m
>    }
> }
>
> constructors.d(34): Error: constructor constructors.A.this (int x) is not
> callable using argument types ()
>

This is my new once-a-day bug :(
Using a function alias, and being unable to call properties on it, because
DMD thinks I'm calling it. Man, it's no property, just a name!

Anyway, just pragma(msg, m) works, strangely.
I think I found a way to use m, somewhat:

void main() {
   foreach (m; __traits(getOverloads, A, "__ctor")) {
       pragma(msg, m); // it thinks I'm calling m
       typeof(&m) tmp = &m;
        writeln( (ParameterTypeTuple!tmp).stringof); // (int), (double),
(string)
        writeln( (ParameterTypeTuple!m).stringof); // (int), (int), (int)
        writeln( typeof(&m).stringof); // A function(int x), A
function(double x), A function(string s)
   }
}

using ParameterTypeTuple!m directly does not differentiate the m's. But using a temporary pointer, it seems to work.

Oh and I even get the arguments names !


Philippe

Philippe Sigaud:
> This is my new once-a-day bug :(

Add them all to Bugzilla :-)

Bye,
bearophile

On Fri, Aug 6, 2010 at 19:09, bearophile <bearophileHUGS@lycos.com> wrote:

> Philippe Sigaud:
> > This is my new once-a-day bug :(
>
> Add them all to Bugzilla :-)
>

I do, from time to time. But I'm never sure if it's a bug or not.

It's related to The Great And Neverending Property Debate (tm). So I don't
what to believe.


Philippe

Philippe Sigaud wrote:

> On Fri, Aug 6, 2010 at 11:43, Rory Mcguire <rjmcguire@gm_no_ail.com> wrote:
> 
> 
>> I've been trying to make a template for this but it seems that dmd still
>> won't allow me to get the parameters of the constructors. dmd Seems to
>> think
>> that I'm trying to use it as a property.
>>
>>
> 
>> void main() {
>>    foreach (m; __traits(getOverloads, A, "__ctor")) {
>>        pragma(msg, m.stringof); // it thinks I'm calling m
>>    }
>> }
>>
>> constructors.d(34): Error: constructor constructors.A.this (int x) is not
>> callable using argument types ()
>>
> 
> This is my new once-a-day bug :(
> Using a function alias, and being unable to call properties on it, because
> DMD thinks I'm calling it. Man, it's no property, just a name!
> 
> Anyway, just pragma(msg, m) works, strangely.
> I think I found a way to use m, somewhat:
> 
> void main() {
>    foreach (m; __traits(getOverloads, A, "__ctor")) {
>        pragma(msg, m); // it thinks I'm calling m
>        typeof(&m) tmp = &m;
>         writeln( (ParameterTypeTuple!tmp).stringof); // (int), (double),
> (string)
>         writeln( (ParameterTypeTuple!m).stringof); // (int), (int), (int)
>         writeln( typeof(&m).stringof); // A function(int x), A
> function(double x), A function(string s)
>    }
> }
> 
> using ParameterTypeTuple!m directly does not differentiate the m's. But using a temporary pointer, it seems to work.
> 
> Oh and I even get the arguments names !
> 
> 
> Philippe

Thanks!! works now. Now we just need to be able to select which constructors we actually want.

string inheritconstructors_helper(alias T)() {
    string s;
    foreach (m; __traits(getOverloads, T, "__ctor")) {
        string args, args1;
        foreach (i, cons; ParameterTypeTuple!(typeof(&m))) {
            pragma(msg, cons.stringof);
            args ~= ","~cons.stringof~" v"~to!string(i);
            args1 ~= ",v"~to!string(i);
        }
        args = args.length < 1 ? args : args[1..$];
        args1 = args1.length < 1 ? args1 : args1[1..$];
        s ~= "this("~args~") { super("~args1~"); }\n";
    }
    return s;
}

class A {
    int i;
    //private this() {}
    this(int x) {
        i = x;
    }
    this(float x) {
        i = cast(int)x; // ignore bad code
    }
    this(string s, int mul) { // test multiple args
        i = to!int(s) * mul;
    }
}
class B : A {
    mixin(inheritconstructors_helper!A());
//  InheritConstructors!A;
}



void main() {
    A a = new B(4);
    a = new B("42", 2);
}

Rory Mcguire wrote:

> Philippe Sigaud wrote:
> 
>> On Fri, Aug 6, 2010 at 11:43, Rory Mcguire <rjmcguire@gm_no_ail.com> wrote:
>> 
>> 
>>> I've been trying to make a template for this but it seems that dmd still
>>> won't allow me to get the parameters of the constructors. dmd Seems to
>>> think
>>> that I'm trying to use it as a property.
>>>
>>>
>> 
>>> void main() {
>>>    foreach (m; __traits(getOverloads, A, "__ctor")) {
>>>        pragma(msg, m.stringof); // it thinks I'm calling m
>>>    }
>>> }
>>>
>>> constructors.d(34): Error: constructor constructors.A.this (int x) is
>>> not callable using argument types ()
>>>
>> 
>> This is my new once-a-day bug :(
>> Using a function alias, and being unable to call properties on it,
>> because DMD thinks I'm calling it. Man, it's no property, just a name!
>> 
>> Anyway, just pragma(msg, m) works, strangely.
>> I think I found a way to use m, somewhat:
>> 
>> void main() {
>>    foreach (m; __traits(getOverloads, A, "__ctor")) {
>>        pragma(msg, m); // it thinks I'm calling m
>>        typeof(&m) tmp = &m;
>>         writeln( (ParameterTypeTuple!tmp).stringof); // (int), (double),
>> (string)
>>         writeln( (ParameterTypeTuple!m).stringof); // (int), (int), (int)
>>         writeln( typeof(&m).stringof); // A function(int x), A
>> function(double x), A function(string s)
>>    }
>> }
>> 
>> using ParameterTypeTuple!m directly does not differentiate the m's. But using a temporary pointer, it seems to work.
>> 
>> Oh and I even get the arguments names !
>> 
>> 
>> Philippe
> 
> Thanks!! works now. Now we just need to be able to select which constructors we actually want.
> 
> string inheritconstructors_helper(alias T)() {
>     string s;
>     foreach (m; __traits(getOverloads, T, "__ctor")) {
>         string args, args1;
>         foreach (i, cons; ParameterTypeTuple!(typeof(&m))) {
>             pragma(msg, cons.stringof);
>             args ~= ","~cons.stringof~" v"~to!string(i);
>             args1 ~= ",v"~to!string(i);
>         }
>         args = args.length < 1 ? args : args[1..$];
>         args1 = args1.length < 1 ? args1 : args1[1..$];
>         s ~= "this("~args~") { super("~args1~"); }\n";
>     }
>     return s;
> }
> 
> class A {
>     int i;
>     //private this() {}
>     this(int x) {
>         i = x;
>     }
>     this(float x) {
>         i = cast(int)x; // ignore bad code
>     }
>     this(string s, int mul) { // test multiple args
>         i = to!int(s) * mul;
>     }
> }
> class B : A {
>     mixin(inheritconstructors_helper!A());
> //  InheritConstructors!A;
> }
> 
> 
> 
> void main() {
>     A a = new B(4);
>     a = new B("42", 2);
> }

Got selection working:

string inheritconstructors_helper(alias T,Selectors...)() {
    string s;

    foreach (m; __traits(getOverloads, T, "__ctor")) {
        string args, args1;
        pragma(msg, typeof(&m));
        /*foreach (sel; Selectors) {
            pragma(msg, sel, is (sel == typeof(&m)));
            continue top;
        }*/
        if (staticIndexOf!(typeof(&m), Selectors)==-1) {
            continue;
        }
        foreach (i, cons; ParameterTypeTuple!(typeof(&m))) {
            pragma(msg, cons.stringof);
            args ~= ","~cons.stringof~" v"~to!string(i);
            args1 ~= ",v"~to!string(i);
        }
        args = args.length < 1 ? args : args[1..$];
        args1 = args1.length < 1 ? args1 : args1[1..$];
        s ~= "this("~args~") { super("~args1~"); }\n";
    }
    return s;
}



Usage:

class B : A {
    mixin(inheritconstructors_helper!(A,TypeTuple!(A function(string,int)
			,A function(int)))());
}