[LLVMbugs] [Bug 20739] explicitly instantiating an overloaded template function instantiates the wrong function

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20739

Richard Smith <richard-llvm at metafoo.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |richard-llvm at metafoo.co.uk
         Resolution|---                         |INVALID

--- Comment #2 from Richard Smith <richard-llvm at metafoo.co.uk> ---
Explicitly-specified template arguments are substituted before template
argument deduction is performed; see 14.8.2 paragraphs 2-5. Therefore, when
Clang sees

template unsigned long & thrust::get <2, unsigned long,
X>(thrust::detail::cons<unsigned long, X> &);

[with X = thrust::detail::cons<unsigned long, thrust::detail::cons<unsigned
long, thrust::null_type> >]

... it will try substituting <2, unsigned long, ...> into each declaration of
'get' before it considers whether the parameter types can match. And
substituting into the declaration on line 126...

template<unsigned int N, typename T1, typename T2>
  inline
    typename tuple_element<N, pair<T1,T2> >::type &
      get(pair<T1,T2> &p)

... produces the type 'tuple_element<2, pair<unsigned long, X> >::type', which
triggers the instantiation of 'tuple_element<2, pair<unsigned long, X> >',
which results in an error outside the immediate context of the substitution.

Therefore your code is ill-formed.

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