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                        <h1 id="use-function-pointers"><a class="header" href="#use-function-pointers">use function pointers</a></h1>
<p>using typedef we can create alias for functions but we can do it in 2 ways</p>
<p>function pointers is as fast as lambdas but faster than std::function objects.</p>
<pre><code class="language-c++">
#include &lt;print&gt;

// not common but function type - use it with *
typedef int Fn(char const*, char const*);
// classic
typedef int (*FN)(char const*, char const*);

// or

// using Fn = int(char const*, char const*);
// using FN = int (*)(char const*, char const*);
// using FnA = auto (*)(char const*, char const*) -&gt; int;

int cmp(char const* src, char const* dst) {
    if (src == nullptr &amp;&amp; dst == nullptr)
        return 0;
    else if (src == nullptr)
        return -1;
    else if (dst == nullptr)
        return 1;
    else {
        while (*src != '\0' &amp;&amp; *dst != '\0') {
            if (*src != *dst) {
                if (*src &gt; *dst)
                    return 1;
                else
                    return -1;
            }
            src++;
            dst++;
        }
        if (*src != '\0' &amp;&amp; *dst == '\0')
            return 1;
        else if (*src == '\0' &amp;&amp; *dst != '\0')
            return -1;
    }
    return 0;
}
int main() {
    Fn* fptr = cmp;
    Fn&amp; fn = cmp;
    FN fp = cmp;
    std::println("{} {} {}", fptr("hakan", "haka"), fp("hakan", "haka"),
                 fn("hakna", "haka"));
    return 0;
}

</code></pre>
<h2 id="unique_ptr-as-callables"><a class="header" href="#unique_ptr-as-callables">unique_ptr as callables</a></h2>
<p>let's try it by using unique_ptr</p>
<pre><code class="language-c++">#include &lt;functional&gt;
#include &lt;memory&gt;
#include &lt;print&gt;

using cb_t = void (*)(int, char const*);

void foo(int id, char const* name) { std::println("{} {}", id, name); }

// this is class template so ctor(T&amp;&amp;) means real rvalues - not extended to lvalue references
template &lt;class Fn&gt;
struct callback {
    callback(Fn&amp;&amp; fn)
        : _fptr{std::make_unique&lt;Fn&gt;(std::forward&lt;Fn&gt;(fn))} {
    }  // use forward with forwarded references always

    template &lt;class... Args&gt;
    void operator()(Args&amp;&amp;... args) {
        std::invoke(*_fptr, std::forward&lt;Args&gt;(args)...);
    }

    template &lt;class... Args&gt;
    void operator()(Args&amp;&amp;... args) const {
        std::invoke(*_fptr, std::forward&lt;Args&gt;(args)...);
    }

    std::unique_ptr&lt;Fn&gt; _fptr;
};

int main() {
    // without cb_t : it fails
    callback&lt;cb_t&gt; cb{foo};

    cb(0, "hakan gedek");

    return 0;
}

</code></pre>
<h2 id="c-style-callbacks"><a class="header" href="#c-style-callbacks">c-style callbacks</a></h2>
<pre><code class="language-c++">struct event_handler {
    typedef void (*start)(int, char const*);
    typedef void (*pause)(int, char const*);
    typedef void (*end)(char const*);
    start _start;
    pause _pause;
    end _end;
};

void start(int id, char const* name) {
    std::println("started {} {}", id, name);
}

void pause(int id, char const* name) { std::println("paused {} {}", id, name); }

void end(char const* name) { std::println("ended {}", name); }

int main() {
    event_handler handler;
    handler._start = start;
    handler._pause = pause;
    handler._end = end;
    handler._start(0, "hakan");
    handler._pause(0, "hakan");
    handler._end("hakan");

    std:println("{} {} {}", sizeof(handler._start), sizeof(handler._pause),
                 sizeof(handler._end));

}
</code></pre>
<pre><code class="language-c++">
started 0 hakan
paused 0 hakan
ended hakan
8 8 8
</code></pre>

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