clang-cl doesn't accept two implicit conversions with a smart pointer pattern in the same way that MSVC does #21195
Comments
I'm surprised that they allow that (it seems to compile with the 14 CTP too). Unless we really can't avoid it, I don't think we should support this. For smart pointers, I think the common thing to do is to provide templates for converting copy constructors and assignment operators, something like: template SP { I'll mark this wontfix for now. |
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Agreed on the wontfix, FWIW I fixed this issue on our side, just filed this so that we have a record of the issue! |
Quuxplusone
added
the
wontfix
Extended Description
$ cat test.cpp
template
struct SP {
SP();
SP(T*);
void operator=(T*);
operator T*();
};
struct B{};
struct D:B{};
void f() {
SP d;
SP 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' to 'SP'
SP b = d;
^ ~
test.cpp(2,8) : note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'SP' to 'const SP &' for 1st
argument
struct SP {
^
test.cpp(2,8) : note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'SP' to 'SP &&' for 1st argument
struct SP {
^
test.cpp(4,3) : note: candidate constructor not viable: no known conversion from 'SP' 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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