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POTop-level const doesn't influence a function signature
 

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  1. POTop-level const doesn't influence a function signature
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    <p>From the C++ Primer 5th Edition, it says:</p> <pre><code>int f(int){ /* can write to parameter */} int f(const int){ /* cannot write to parameter */} </code></pre> <p>The two functions are <strong>indistinguishable</strong>. But as you know, the two functions really differ in how they can update their parameters.</p> <p>Can someone explains to me?</p> <hr> <p><strong>EDIT</strong><br> I think I didn't interpret my question well. What I really care is why C++ doesn't allow these two functions simultaneously as different function since they are really different as to "whether parameter can be written or not". Intuitively, it should be!</p> <hr> <p><strong>EDIT</strong><br> The nature of <em>pass by value</em> is actually <em>pass by coping argument values to parameter values</em>. Even for <em>references</em> and <em>pointers</em> where thee copied values are <em>addresses</em>. From the caller's viewpoint, whether <em>const</em> or <em>non-const</em> is passed to the function does not influence values (and of course types of) copied to parameters.<br> The distinction between <strong>top-level const</strong> and <strong>low-level const</strong> matters when copying objects. More specifically, <strong>top-level const</strong>(not the case of <strong>low-level const</strong>) is ignored when copying objects since copying won't influence the copied object. It is immaterial whether the object copied to or copied from is <em>const</em> or not.<br> So for the caller, differentiating them is not necessary. Likely, from the function viewpoint, the <em>top-level const</em> parameters doesn't influence the interface and/or the functionality of function. The two function actually accomplish the same thing. Why bother implementing two copies?</p>
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    1. COThey're indistinguishable to the caller. It shouldn't have to care whether they modify their own copies.
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    2. COIf you were talking about references or pointers, it'd be a different story
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    3. COIf you don't add "`&`", then the `const` is useless, since the arguments are copied. In another case, `int f(int &)` vs `int f(const int &)` would be distinguishable, and useful.
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