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    <p>This type of operation is actually the basis for implementing the constant reoccurring template pattern, where inside the base-class you actually <code>static_cast</code> the <code>this</code> pointer of the base-class to the derived-class template type. Since <code>S</code> is an unambiguous base class of <code>T</code>, and you are not accessing any members from the <code>static_cast</code> that are not already members of <code>S</code>, I don't see why you would encounter any issues.</p> <p>Section 5.2.8 on static casting in paragraph 5 states:</p> <blockquote> <p>An lvalue of type “<em>cv1</em> B”, where B is a class type, can be cast to type “reference to <em>cv2</em> D”, where D is a class derived (clause 10) from B, if a valid standard conversion from “pointer to D” to “pointer to B” exists (4.10), <em>cv2</em> is the same cv-qualification as, or greater cv-qualification than, <em>cv1</em>, and B is not a virtual base class of D. The result is an lvalue of type “<em>cv2</em> D.” If the lvalue of type “<em>cv1</em> B” is actually a sub-object of an object of type D, the lvalue refers to the enclosing object of type D. Otherwise, the result of the cast is undefined.</p> </blockquote> <p>You seem to be meeting all the requirements that avoid undefined behavior. That is:</p> <ol> <li>Class <code>T</code> is derived from <code>S</code></li> <li>A pointer conversion from <code>S</code> to <code>T</code> does exist since <code>S</code> is both accessible and an unambiguous base-class of <code>T</code> (requirements from 4.10)</li> <li>You are using the same constant-value-qualification for both types</li> <li><code>S</code> is not a virtual base-class of <code>T</code></li> </ol>
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    1. POwhat standard says about static casting to temporary inheritor?
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    1. COI've never understood the ability of static_cast to cast to a more derived type. In this case it's clear that `s` *is not* a `T`, which could be easily demonstrated by adding another member variable to `T`.
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      1. USMark Ransom
    2. COYou can make the cast, but accessing a non-existent member is going to invoke undefined behavior. I believe in this regard it's pretty-much trying to mirror C-style casting, where you can cast from any pointer type to any other pointer type. The results of the cast itself are not undefined, but trying to access a non-existent `struct` member in the cast pointer for instance would result in undefined behavior.
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