c++ how to assert that all std::shared_ptr in a vector are referring to something

问题

When I have a function receiving a (smart) pointer that is supposed to refer something, I always start as follows:

class Foo;
void doSomething(const std::shared_ptr<Foo>& pFoo)
{
    assert(pFoo);
    // ...
}

Now I am looking for a similar assert condition for a vector (or other container) of (smart) pointers. The best I could come up with is:

void doSomething(const std::vector<std::shared_ptr<Foo> >& pFoos)
{
    assert(std::all_of(pFoos.begin(), pFoos.end(), [](const std::shared_ptr<Foo>& pFoo) { return pFoo; }));
    // ...
}

I wonder whether this could be improved.. can the lambda be avoided? (I tried to use the get() method of shared_ptr but template deduction fails then) Or is there another way to assert for a whole container?

回答1:

one more way to do it:

assert(std::find(pFoos.begin(), pFoos.end(), nullptr) == pFoos.end());

回答2:

Another slightly convoluted way to express it with standard functionality only:

assert(std::none_of(pFoos.begin(), pFoos.end(), std::logical_not<std::shared_ptr<Foo>>{}));

From C++14 onwards, you can use the generic specialization of std::logical_not:

assert(std::none_of(pFoos.begin(), pFoos.end(), std::logical_not<>{}));

回答3:

You could use implement your own utility predicate:

struct is_nullptr
{
    template <typename T>
    bool operator()(T&& x) const noexcept { return x == nullptr; }
};

void doSomething(const std::vector<std::shared_ptr<Foo> >& pFoos)
{
    assert(!std::any_of(pFoos.begin(), pFoos.end(), is_nullptr{});
    // ...
}

And/or your own "range assertion":

template <typename TContainer, typename TPredicate>
void range_assert(TContainer&& container, TPredicate&& p)
{
    for(auto&& x : container)
    {
        assert(p(x));
    }
}

void doSomething(const std::vector<std::shared_ptr<Foo> >& pFoos)
{
    range_assert(pFoos, [](const std::shared_ptr<Foo>& x) { return x; });
    // ...
}

来源：https://stackoverflow.com/questions/41037465/c-how-to-assert-that-all-stdshared-ptr-in-a-vector-are-referring-to-somethin

标签

c++

c++11

vector

shared-ptr

assert