http://llvm.org/bugs/show_bug.cgi?id=18740
Bug ID: 18740
Summary: Unhelpful error message when attempting to deduce an
initializer list in a template context
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++11
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
I have the following code:
-----
#include <vector>
#define RETURNS(...) -> decltype((__VA_ARGS__)) { return (__VA_ARGS__); }
template <typename This, typename... Args>
auto fun(This &&this_, Args&&... args)
RETURNS(this_.fun(std::forward<Args>(args)...))
struct X
{
void fun(std::vector<int> v) {}
};
int main()
{
X x;
fun(x, {1, 2, 3});
}
-----
When compiling, this yields the following errors:
-----
subst.cpp:16:5: error: no matching function for call to 'fun'
fun(x, {1, 2, 3});
^~~
subst.cpp:6:6: note: candidate template ignored: substitution failure [with
This
= X &, Args = <>]: too few arguments to function call, single argument
'v'
was not specified
auto fun(This &&this_, Args&&... args)
RETURNS(this_.fun(std::forward<Args>(args)...))
^
~
1 error generated.
-----
As I understand (from the discussion in
http://stackoverflow.com/questions/21573808/using-initializer-lists-with-variadic-templates),
the initializer list could not be deduced. This is not clear in the message,
however, especially with the (IMO) misleading "Args = <>".
Note: reversing the order of declaration of fun<> and struct X instead yields
the following equally misleading error message (because yes it was, right
there!)
-----
subst.cpp:17:5: error: no matching function for call to 'fun'
fun(x, {1, 2, 3});
^~~
subst.cpp:12:6: note: candidate template ignored: substitution failure [with
This = X &, Args = <>]: too few arguments to function call, single
argument 'v' was not specified
auto fun(This &&this_, Args&&... args)
RETURNS(this_.fun(std::forward<Args>(args)...))
^
~
1 error generated.
-----
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