[PATCH] D15421: [Feature] Add a builtin for indexing into parameter packs

[Richard Smith via cfe-commits]

rsmith added inline comments.

================
Comment at: include/clang/Basic/Builtins.h:216-219
@@ -215,3 +215,6 @@
   /// \brief This names the __make_integer_seq BuiltinTemplateDecl.
   BTK__make_integer_seq
+
+  /// \brief This names the __nth_element BuiltinTemplateDecl.
+  , BTK__nth_element
 };
----------------
Please put the comma after `BTK__make_integer_seq`, not on this line.

================
Comment at: lib/AST/DeclTemplate.cpp:1243
@@ +1242,3 @@
+static TemplateParameterList *
+createNthElement(const ASTContext &C, DeclContext *DC) {
+  // typename IndexType
----------------
Rename this `createNthElementParameterList`.

================
Comment at: lib/AST/DeclTemplate.cpp:1244-1248
@@ +1243,7 @@
+createNthElement(const ASTContext &C, DeclContext *DC) {
+  // typename IndexType
+  auto *IndexType = TemplateTypeParmDecl::Create(
+      C, DC, SourceLocation(), SourceLocation(), /*Depth=*/0, /*Position=*/0,
+      /*Id=*/nullptr, /*Typename=*/true, /*ParameterPack=*/false);
+  IndexType->setImplicit(true);
+
----------------
Use `NonTypeTemplateParmDecl::Create`. You can get `size_t` from `ASTContext::getSizeType`.

================
Comment at: lib/Sema/SemaTemplate.cpp:2102-2103
@@ +2101,4 @@
+    // We simply return the type at index `Index`.
+    // TODO:
+    // What are the implications of calling .getExtValue() on an APSInt?
+    assert(Index.getExtValue() == Index &&
----------------
`getExtValue` is OK here, as we don't support `size_t` being larger than 64 bits.


http://reviews.llvm.org/D15421