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Implement the part of C++0x [temp.arg.explicit]p3 that pertains to 

parameter packs. In particular, a parameter pack not otherwise deduced
is deduced to an empty parameter pack.

The C++0x wording here is a bit unfortunate; this should really only
apply to function templates, and it mentions "trailing" parameter
packs, which doesn't really make sense in the context of function
templates. Will file a core issue separately.

llvm-svn: 122463
This commit is contained in:
Douglas Gregor 2010-12-23 01:52:01 +00:00
parent 18b762a946
commit ca4d91d9f6
2 changed files with 38 additions and 1 deletions
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12
clang/lib/Sema/SemaTemplateDeduction.cpp
View File

@ -1708,9 +1708,10 @@ Sema::FinishTemplateArgumentDeduction(FunctionTemplateDecl *FunctionTemplate,
// [...] or if any template argument remains neither deduced nor
// explicitly specified, template argument deduction fails.
llvm::SmallVector<TemplateArgument, 4> Builder;
for (unsigned I = 0, N = Deduced.size(); I != N; ++I) {
for (unsigned I = 0, N = Deduced.size(); I != N; ++I) {
// FIXME: Variadic templates. Unwrap argument packs?
NamedDecl *Param = FunctionTemplate->getTemplateParameters()->getParam(I);
if (!Deduced[I].isNull()) {
if (I < NumExplicitlySpecified) {
// We have already fully type-checked and converted this
@ -1777,6 +1778,15 @@ Sema::FinishTemplateArgumentDeduction(FunctionTemplateDecl *FunctionTemplate,
continue;
}
// C++0x [temp.arg.explicit]p3:
// A trailing template parameter pack (14.5.3) not otherwise deduced will
// be deduced to an empty sequence of template arguments.
// FIXME: Where did the word "trailing" come from?
if (Param->isTemplateParameterPack()) {
Builder.push_back(TemplateArgument(0, 0));
continue;
}
// Substitute into the default template argument, if available.
TemplateArgumentLoc DefArg

27
clang/test/CXX/temp/temp.fct.spec/temp.arg.explicit/p3-0x.cpp Normal file
View File

@ -0,0 +1,27 @@
// RUN: %clang_cc1 -std=c++0x -fsyntax-only -verify %s
namespace ParameterPacksWithFunctions {
template<typename ...> struct count;
template<typename Head, typename ...Tail>
struct count<Head, Tail...> {
static const unsigned value = 1 + count<Tail...>::value;
};
template<>
struct count<> {
static const unsigned value = 0;
};
template<unsigned> struct unsigned_c { };
template<typename ... Types>
unsigned_c<count<Types...>::value> f();
void test_f() {
unsigned_c<0> uc0a = f(); // okay, deduced to an empty pack
unsigned_c<0> uc0b = f<>();
unsigned_c<1> uc1 = f<int>();
unsigned_c<2> uc2 = f<float, double>();
}
}