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Re: Virtual base constructor arguments and constructor delegation

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On 5/8/2022 11:45 AM, Marcel Mueller wrote:
> Am 07.05.22 um 14:25 schrieb Alf P. Steinbach:

<snip>

>> While the details you sketch may be impossible the general idea is not 
>> impossible.
>>
>> Just the idea you sketched of dummy initialization, but with slightly 
>> different details:
>>
>>
>> #include <tuple>
>> using   std::ignore;
>>
>> using C_str = const char*;
>>
>> class Interpolation
>> {
>> protected:
>>      struct Dummy_init {};
>>      Interpolation( Dummy_init ) { throw 666; }
> 
> Hmm, this at least prevents accidental default initialization.
> I think the additional classes of your example are not really required 
> for this to work. Although I dislike functions that should never be called.
> 
> 
> I did not need virtual inheritance very often and probably never with a 
> non default constructor so far. But since a virtual base can only be 
> initialized by the deepest class I expected some syntax to declare 
> "incomplete" constructors that can only be used for derived classes.
> Something like
> 
> class PolarInterpolation : public virtual Interpolation
> {protected:
>     PolarInterpolation() = 0 {}
> 

What's wrong with:

class Interpolation
{
protected:
     // struct Dummy_init {};
     Interpolation( ); // decl only

public:
     Interpolation( const int count ) { ignore = count; }
};

and get rid of all
//      Interpolation( Dummy_init() )
and replace with:
         : Interpolation( )


This wouldn't work if you need to have a Interpolation( ) constructor 
that needs to be legitimately called somewhere else, however the obvious 
idea is to use a constructor that is declared but not defined.

> 
> Marcel

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Thread

Virtual base constructor arguments and constructor delegation Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-05-07 13:24 +0200
  Re: Virtual base constructor arguments and constructor delegation "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-07 14:25 +0200
    Re: Virtual base constructor arguments and constructor delegation Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-05-08 11:45 +0200
      Re: Virtual base constructor arguments and constructor delegation Manfred <noname@add.invalid> - 2022-05-08 18:56 +0200
        Re: Virtual base constructor arguments and constructor delegation "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-09 00:18 +0200
          Re: Virtual base constructor arguments and constructor delegation Manfred <noname@add.invalid> - 2022-05-09 14:56 +0200
  Re: Virtual base constructor arguments and constructor delegation Sam <sam@email-scan.com> - 2022-05-08 09:34 -0400

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