changes

[user706]

• fix gcc warning warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

  with 2 lines splitup:

     Concept *cpt = reinterpret_cast<Concept*>(memory);
     cpt->~Concept();

• use std::size_t instead of unsigned
• align according to alignof(std::max_align_t)
• use mutable F to get the following functor compiled:

    struct Func1
    {
        int operator()(int val) // const
        {
           return val * 2;
        }

    int a[10];
    };

(used here: https://github.com/user706/CxxFunctionBenchmark).
I knew what to do here, thanks to @arobenko - ref

• use static_assert instead of enable_if
• add: SmallFun& operator=(F const&f)

[user706]

You can see it in action in the following benchmark:
https://github.com/user706/CxxFunctionBenchmark
(used in various.cpp)

PS: what commands do I have to use, to get this buckaroo thing working?

Thanks!

[user706]

I'm compiling with gcc under Linux. Which compiler do you use?
Does it compile with your compiler?

Are my changes with static_asserts working in your setup?

[nikhedonia]

Thanks for your efforts!

Are my changes with static_asserts working in your setup?

The enable_if vs static_assert is always an interesting discussion.
Although static_assert is easier to read and understand, it has one big disadvantage:
You cannot use it in a SFINAE context.
Hence we cannot use it here and have to patiently wait for the Concepts-TS to be adopted before we can make it more sane and readable.

use mutable F to get the following functor compiled:

It works for your use case but it would break other cases.
Imagine a functor that has different implementations of operator().
Using mutable will always prefer the non-const variant even if in a const context.

Checkout the godbolt example and see how the return value of T::operator() changes based on the presence of the mutable keyword.

In order to handle both situations correctly, we need a smarter approach.

As of the alignment issue, good spot! Would love to get that merged.
Can you make a PR with only the following changes:

• fix gcc warning warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
• use std::size_t instead of unsigned
• align according to alignof(std::max_align_t)

[user706]

The enable_if vs static_assert is always an interesting discussion.
Although static_assert is easier to read and understand, it has one big disadvantage:
You cannot use it in a SFINAE context.

?
Which SFINAE use-case do you mean exactly?
Please can you give an example where your enable_if is useful for a user using the smallfun library.

[user706]

Imagine a functor that has different implementations of operator().
Using mutable will always prefer the non-const variant even if in a const context.

Checkout the godbolt example and see how the return value of T::operator() changes based on the presence of the mutable keyword.

(edited)

Your example needs fixing ;)

    {
        T t{};
        smallfun::SmallFun<int()> f(t);
        std::cout << f() << "\t should get " << t() << std::endl;
    }
    {
        const T t{};
        smallfun::SmallFun<int()> f(t);
        std::cout << f() << "\t should get " << t() << std::endl;
    }

See it here on wandbox, to see how your original code (on the master branch) also does not return what you want.

I'll need to research, to see how to get it to do what we actually want...

Sorry... I just noticed that this is probably not a problem, since std::function behaves exactly the same way. See here

(Oh and by the way... std::function also does not behave the way you suspected in your godbolt example. See here)

Interesting reading here:
"std::function does not enforce const-correctness: it allows you to store mutable callables"

[user706]

(edited)

I should also mention that the following

add: SmallFun& operator=(F const&f)

(ref) is important!

It's one way to fix a bug in your original, where a destructor is not called.
See it your original here -- prints dtor only once, but should come twice.

The fix is to uncomment line 3

#include "smallfun_changed.hpp" /* mine */

-- it should then print dtor twice.

[user706]

I've got a branch called my_experiments: https://github.com/user706/smallfunction/tree/my_experiments
Still working on this (when I find time). (Still need to experiment some more, and fix some stuff that's still open... such as fixing the rhs after move operations, etc. )