Add explicit to single-parameter constructors

[NewbieOrange]

Describe the new feature

Can we add explicit to single-parameter constructors to avoid unintended implicit construct?

Code example

    explicit thread_pool(const ui32 &_thread_count = std::thread::hardware_concurrency())
        : thread_count(_thread_count ? _thread_count : std::thread::hardware_concurrency()), threads(new std::thread[thread_count]);
// ...
    explicit synced_stream(std::ostream &_out_stream = std::cout);

[bshoshany]

Thanks for the suggestion! I'm not opposed to adding the explicit keyword, but given that there is only one constructor for each of these classes, under what circumstances will implicit constructors be an issue?

[NewbieOrange]

To disallow passing an uint32 to a function taking, for example, thread_pool as a const ref, therefore forcing users to explicitly call the constructor to avoid confusion or unintended object construction.

[bshoshany]

I'm still not convinced. Would you mind writing a short code example illustrating a case where this might be relevant? Thanks!

[NewbieOrange]

It may be a silly error, but:

std::uint32_t thread_cnt = 10;
thread_pool thread_pool{thread_cnt};

void f(const thread_pool& pool) {
  // do something
}

f(thread_cnt); // error-prone, passed wrong parameter but still compiles

[bshoshany]

Okay, I see what you mean. I'll add this to my TODO list, but it will only be added when the new version is released (which will have many other changes and new features). It might take a few weeks or even months since I'm really busy these days with teaching and research. Thanks for your contribution!