e4e9e281a1
Summary: [expr.cast.static] states: > 3. A glvalue of type “cv1 T1” can be cast to type “rvalue reference to cv2 T2” if “cv2 T2” is reference-compatible > with “cv1 T1”. The result refers to the object or the specified base class subobject thereof. If T2 is > an inaccessible or ambiguous base class of T1, a program that necessitates such a cast is > ill-formed. > > 4. Otherwise, an expression e can be explicitly converted to a type T using a static_cast of the form static_- > cast<T>(e) if the declaration T t(e); is well-formed, for some invented temporary variable t. [...] Currently when checking p3 Clang will diagnose `static_cast<T&&>(e)` as invalid if the argument is not reference compatible with `T`. However I believe the correct behavior is to also check p4 in those cases. For example: ``` double y = 42; static_cast<int&&>(y); // this should be OK. 'int&& t(y)' is well formed ``` Note that we still don't check p4 for non-reference-compatible types which are reference-related since `T&& t(e);` should never be well formed in those cases. Reviewers: rsmith Subscribers: cfe-commits Differential Revision: https://reviews.llvm.org/D26231 llvm-svn: 285872
44 lines
1.9 KiB
C++
44 lines
1.9 KiB
C++
// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
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// p3
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// A glvalue of type "cv1 T1" can be cast to type "rvalue reference to
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// cv2 T2" if "cv2 T2" is reference-compatible with "cv1 T1" (8.5.3).
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// p4
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// Otherwise, an expression e can be explicitly converted to a type T using a
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// static_cast of the form static_cast<T>(e) if the declaration T t(e); is
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// well-formed, for some invented temporary variable t (8.5). [...]
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struct A { };
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struct B : A { };
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struct C { explicit operator A&&(); };
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struct D { operator B(); };
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template<typename T> T& lvalue();
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template<typename T> T&& xvalue();
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template <typename T> T prvalue();
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void test(A &a, B &b) {
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A &&ar0 = static_cast<A&&>(prvalue<A>());
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A &&ar1 = static_cast<A&&>(prvalue<B>());
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A &&ar2 = static_cast<A&&>(lvalue<C>());
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A &&ar3 = static_cast<A&&>(xvalue<C>());
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A &&ar4 = static_cast<A&&>(prvalue<C>());
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A &&ar5 = static_cast<A&&>(lvalue<D>());
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A &&ar6 = static_cast<A&&>(xvalue<D>());
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A &&ar7 = static_cast<A&&>(prvalue<D>());
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A &&ar8 = static_cast<A&&>(prvalue<const A>()); // expected-error {{binding value of type 'const A' to reference to type 'A' drops 'const' qualifier}}
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A &&ar9 = static_cast<A&&>(lvalue<const A>()); // expected-error {{cannot cast from lvalue of type 'const A'}}
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A &&ar10 = static_cast<A&&>(xvalue<const A>()); // expected-error {{cannot cast from rvalue of type 'const A'}}
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const A &&ar11 = static_cast<const A&&>(prvalue<A>());
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const A &&ar12 = static_cast<const A&&>(prvalue<B>());
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const A &&ar13 = static_cast<const A&&>(lvalue<C>());
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const A &&ar14 = static_cast<const A&&>(xvalue<C>());
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const A &&ar15 = static_cast<const A&&>(prvalue<C>());
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const A &&ar16 = static_cast<const A&&>(lvalue<D>());
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const A &&ar17 = static_cast<const A&&>(prvalue<A const volatile>()); // expected-error {{binding value of type 'const volatile A' to reference to type 'const A' drops 'volatile' qualifier}}
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}
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