http://llvm.org/bugs/show_bug.cgi?id=20821
Bug ID: 20821
Summary: clang-cl doesn't accept two implicit conversions with
a smart pointer pattern in the same way that MSVC does
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
$ cat test.cpp
template<class T>
struct SP {
SP();
SP(T*);
void operator=(T*);
operator T*();
};
struct B{};
struct D:B{};
void f() {
SP<D> d;
SP<B> b = d;
}
$ cl -c test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.61030 for x86
Copyright (C) Microsoft Corporation. All rights reserved.
test.cpp
$ clang-cl -c test.cpp
test.cpp(14,9) : error: no viable conversion from 'SP<D>' to 'SP<B>'
SP<B> b = d;
^ ~
test.cpp(2,8) : note: candidate constructor (the implicit copy constructor)
not viable: no known conversion from 'SP<D>' to 'const SP<B> &' for 1st
argument
struct SP {
^
test.cpp(2,8) : note: candidate constructor (the implicit move constructor)
not viable: no known conversion from 'SP<D>' to 'SP<B> &&' for 1st argument
struct SP {
^
test.cpp(4,3) : note: candidate constructor not viable: no known conversion
from 'SP<D>' to 'B *' for 1st argument
SP(T*);
^
test.cpp(6,3) : note: candidate function
operator T*();
^
1 error generated.
It seems like MSVC first invokes SP::operator T*() and then invokes the ctor
taking the T* from it, which requires another implicit conversion from D* to
B*. I don't think this is valid C++, but we may want to support it for compat
with MSVC.
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