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    <p>NOTE FROM OP: <em>VC++ was buggy. VC++ 2015 accepts the code correctly.</em></p> <p>My original answer that the code that VC++ rejected is disallowed in the standard actually was wrong: It is allowed as Johannes Schaub pointed out: in 5.1 [expr.prim.general] paragraph 12 it is described where an <em>id-expression</em> denoting a non-static data member or a non-static member function can be used. In particular, the last bullet states:</p> <blockquote> <p>if that id-expression denotes a non-static data member and it appears in an unevaluated operand.</p> </blockquote> <p>The expression in <code>decltype(expr)</code> is an unevaluated operand. Furthermore, 9.3.1 [class.mfct.non-static] paragraph 3 explains the situation where <code>this</code> is implicitly added to an expression:</p> <blockquote> <p>When an id-expression (5.1) that is not part of a class member access syntax (5.2.5) and not used to form a pointer to member (5.3.1) is used in a member of class X in a context where this can be used (5.1.1), if name lookup (3.4) resolves the name in the id-expression to a non-static non-type member of some class C, and if either the id-expression is potentially evaluated or C is X or a base class of X, the id-expression is transformed into a class member access expression (5.2.5) using (*this) (9.3.2) as the postfix-expression to the left of the . operator.</p> </blockquote> <p>The context in question is not "potentially evaluated" and there is no based involved. Thus, <code>this</code> isn't added and doesn't have to be in scope. Taken together, this means that the declaration</p> <pre><code>decltype(fwd.rbegin()) begin() const; </code></pre> <p>should be legal. It seems that using</p> <pre><code>decltype(static_cast&lt;Reverser&lt;Fwd&gt; const*&gt;(0)-&gt;fwd.rbegin()) begin() const; </code></pre> <p>is a work-around in cases where the compiler isn't correctly implemented.</p>
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    1. POWhy does the compiler want a trailing return-type?
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    1. POWhy does the compiler want a trailing return-type?
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    1. CO`fwd` is in scope even outside the function definition. Other C++11 compilers handle this just fine. I'd have to look closer at the standard, but I think this is just a VC++ bug.
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    2. COI'm pretty sure that VC++ is correct on this an the other compilers are wrong! What is the syntax of the out-of-line definition of `begin()` if the `decltype()` is **not** trailing?
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    3. COIn a conforming C++ implementation, his code is valid. There will be no `this` added, and consequently there will be no const/volatile modification added by a const/volatile member function, but that's irrelevant here. See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1207
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      1. USJohannes Schaub - litb
 

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