Goals and Priorities for C++

Re:Goals and Priorities for C++ by jcelerier on Friday May 22, 2020 @02:37AM (#23269257)

> Only if you write C++ like Java. But there are also coding styles heavily based on templates, and then the use of multiple, or any inheritance is rare.

It's super common to implement mix-ins, which is as based on templates as it's possible to be, with multiple inheritance, e.g.

    struct featureA { int x; }; 
    struct featureB { const char* foo{}; void print(); };

etc

and then

    template<typename... Args>
    struct mixin: Args... { 
        template<typename... CtorArgs> 
        mixin(CtorArgs... args)
          : Args{args}...
        { }
    };

    using foobar = mixin<featureA, featureB>;
    void f() { foobar{123, "foo"}.print(); }

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Re:Goals and Priorities for C++ by MaxBarraclough on Friday May 22, 2020 @04:57AM (#23269990)

> It's super common

Curiously recurring, even! [0]

Although what you're showing seems to be a variation on the curiously recurring template pattern, as the classes being mixed are listed 'symmetrically' without much regard for which will inherit from which. I found a blog post on 'mixin classes', which are like the CRTP but invert the inheritance relation. [1] What you've shown seems to be a third way.

[0] https://en.wikipedia.org/wiki/Curiously_recurring_template_p...

[1] https://www.fluentcpp.com/2017/12/12/mixin-classes-yang-crtp...

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Re:Goals and Priorities for C++ by jcelerier on Friday May 22, 2020 @05:18AM (#23270114)

yes, it's not proper CRTP but I did not want to spend too much time on that... just show that multiple inheritance has its uses even in fairly generic, non-OOP code :-)

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Re:Goals and Priorities for C++ by gpderetta on Friday May 22, 2020 @09:08AM (#23271603)

CRTP is a common use case. Also inheritance is often used to implement type level recursion (although this is significantly less needed now that we have argument packs).

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