https://llvm.org/bugs/show_bug.cgi?id=25977
Bug ID: 25977
Summary: Poor diagnostic when forgetting to repeat default
template type parameter
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++11
Assignee: unassignedclangb...@nondot.org
Reporter: nicolaswe...@gmx.de
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
Consider this program:
template<typename T> struct DefaultTraits;
template<typename T, typename Traits = DefaultTraits<T>>
struct ScopedTypeRef {
ScopedTypeRef(T object = Traits::InvalidValue()) {}
};
template <typename NST>
struct PointerTraits {
static NST InvalidValue() { return nullptr; }
};
template <typename NST>
class scoped_nsprotocol : public ScopedTypeRef<NST, PointerTraits<NST>> {
public:
using ScopedTypeRef<NST>::ScopedTypeRef;
};
int main() {
scoped_nsprotocol<int*> array(new int);
}
clang complains:
thakis@thakis:~/Downloads$ ~/src/llvm-build/bin/clang -c
templated-inherited-ctor.cc -std=c++11
templated-inherited-ctor.cc:15:9: error: using declaration refers into
'ScopedTypeRef<int *>::', which is not a base class of
'scoped_nsprotocol<int *>'
using ScopedTypeRef<NST>::ScopedTypeRef;
^~~~~~~~~~~~~~~~~~~~
templated-inherited-ctor.cc:19:27: note: in instantiation of template class
'scoped_nsprotocol<int *>' requested here
scoped_nsprotocol<int*> array(new int);
^
templated-inherited-ctor.cc:19:27: error: no matching constructor for
initialization of 'scoped_nsprotocol<int *>'
scoped_nsprotocol<int*> array(new int);
^ ~~~~~~~
templated-inherited-ctor.cc:13:7: note: candidate constructor (the implicit
copy constructor) not viable: no known conversion from
'int *' to 'const scoped_nsprotocol<int *>' for 1st argument
class scoped_nsprotocol : public ScopedTypeRef<NST, PointerTraits<NST>> {
^
templated-inherited-ctor.cc:13:7: note: candidate constructor (the implicit
move constructor) not viable: no known conversion from
'int *' to 'scoped_nsprotocol<int *>' for 1st argument
class scoped_nsprotocol : public ScopedTypeRef<NST, PointerTraits<NST>> {
^
templated-inherited-ctor.cc:13:7: note: candidate constructor (the implicit
default constructor) not viable: requires 0 arguments,
but 1 was provided
2 errors generated.
The fix is to change
using ScopedTypeRef<NST>::ScopedTypeRef;
into
using ScopedTypeRef<NST, PointerTraits<NST>>::ScopedTypeRef;
which isn't very clear from the error. If the base class is a template with
some default args and the default args are not explicitly passed in, then we
could emit a better diagnostic in that case.
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