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    <p>Unfortunately, what you are asking for is impossible with the traditional interface of smart pointers.</p> <p>The issue is one of lifetime. A <code>weak_ptr</code> cannot be use to access the object directly, because it does not guarantee that said object will live long enough: the object might be pulled right from under your feet.</p> <p>Example:</p> <pre><code>int main() { std::shared_ptr&lt;int&gt; sp(new int(4)); std::weak_ptr&lt;int&gt; wp(sp); if (not wp.expired()) { sp.reset(); std::cout &lt;&lt; *wp &lt;&lt; "\n"; // Access WP ? But there is nothing there! } } </code></pre> <p>Thus, for better or worse, there is <em>no other choice</em> than recovering a shared pointer from the weak pointer any time you actually need to access the object <em>without controlling the duration of this access</em>.</p> <hr> <p>This last point, however, is our clue. A simple idea being to write a well-behaved client of <code>weak_ptr</code> yourself and change the way it allows the external world to access the data. For example:</p> <pre><code>template &lt;typename T&gt; class very_weak_ptr { public: very_weak_ptr() {} explicit very_weak_ptr(std::weak_ptr&lt;T&gt; wp): _wp(wp) {} template &lt;typename F&gt; void apply(F&amp;&amp; f) { std::shared_ptr&lt;T&gt; sp = _wp.lock(); f(sp.get()); } private: std::weak_ptr&lt;T&gt; _wp; }; // class very_weak_ptr </code></pre> <p><em>Note: there is one remaining flaw, <code>enable_shared_from_this</code> allows to recover a <code>std::shared_ptr&lt;T&gt;</code> from the very instance of <code>T</code>; you can add a compile time check on <code>T</code> to prevent usage of this class with such objects.</em></p>
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    1. POA very weak reference (cannot be turned into shared)
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    1. USMatthieu M.
    1. USMatthieu M.
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    1. POA very weak reference (cannot be turned into shared)
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    1. COYou know thanks to the second part this is a pretty good answer. You bring a very interesting concept here, the `apply` function, which shelters the scope of shared-ification, lovely idea. However the first part just repeats what I said in the first line of the 4th paragraph in my question. And that is wrong because shared_ptr are not 100% safe (no correctness guarantee under threading, raw pointer leakage through get() or `&(*)`, construction of another ref count class if not using shared_from_this...). You've got to be smart usng smart ptrs. They don't barricade well.
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    2. COWhat I mean to say, is that my "impossible" like you qualify it, is the same level of "impossible" that is already in use with shared_ptr. So I don't accept that as an introduction of an answer. You could remove the whole entire first part and I'd accept it though :). in the meantime you have my upvote.
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    3. CO@v.oddou: You are right, this answer was written "au fil de l'eau" and it showed; I've rewritten part of the text to make it more coherent with itself. As you correctly identified, the key point is controlling the scope in which ownership is shared; though to make it totally safe you would probably need to rewrite a `shared_ptr` implementation *without* the `enable_shared_from_this` backdoor.
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