[c++1z] N4295: fold-expressions.

This is a new form of expression of the form:

  (expr op ... op expr)

where one of the exprs is a parameter pack. It expands into

  (expr1 op (expr2onwards op ... op expr))

(and likewise if the pack is on the right). The non-pack operand can be
omitted; in that case, an empty pack gives a fallback value or an error,
depending on the operator.

llvm-svn: 221573

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/test/Parser/cxx1z-fold-expressions.cpp b/clang/test/Parser/cxx1z-fold-expressions.cpp
new file mode 100644
index 00000000000..a908311ea31
--- /dev/null
+++ b/clang/test/Parser/cxx1z-fold-expressions.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++1z -verify %s
+
+template<typename ...T> constexpr auto sum(T ...t) { return (... + t); }
+template<typename ...T> constexpr auto product(T ...t) { return (t * ...); }
+template<typename ...T> constexpr auto all(T ...t) { return (true && ... && t); }
+template<typename ...T> constexpr auto all2(T ...t) { return (t && ... && true); }
+
+int k1 = (1 + ... + 2); // expected-error {{does not contain any unexpanded parameter packs}}
+int k2 = (1 + ...); // expected-error {{does not contain any unexpanded parameter packs}}
+int k3 = (... + 2); // expected-error {{does not contain any unexpanded parameter packs}}
+
+template<int ...N> void bad1() { (N + ... + N); } // expected-error {{unexpanded parameter packs in both operands}}
+// FIXME: it would be reasonable to support this as an extension.
+template<int ...N> void bad2() { (2 * N + ... + 1); } // expected-error {{expression not permitted as operand}}
+template<int ...N> void bad3() { (2 + N * ... * 1); } // expected-error {{expression not permitted as operand}}
+template<int ...N, int ...M> void bad4(int (&...x)[N]) { (N + M * ... * 1); } // expected-error {{expression not permitted as operand}}
+template<int ...N, int ...M> void fixed4(int (&...x)[N]) { ((N + M) * ... * 1); }
+
+// Parens are mandatory.
+template<int ...N> void bad5() { N + ...; } // expected-error {{expected expression}} expected-error +{{}}
+template<int ...N> void bad6() { ... + N; } // expected-error {{expected expression}}
+template<int ...N> void bad7() { N + ... + N; } // expected-error {{expected expression}} expected-error +{{}}
+
+// Must have a fold-operator in the relevant places.
+template<int ...N> int bad8() { return (N + ... * 3); } // expected-error {{operators in fold expression must be the same}}
+template<int ...N> int bad9() { return (3 + ... * N); } // expected-error {{operators in fold expression must be the same}}
+template<int ...N> int bad10() { return (3 ? ... : N); } // expected-error +{{}} expected-note {{to match}}
+template<int ...N> int bad11() { return (N + ... 0); } // expected-error {{expected a foldable binary operator}} expected-error {{expected expression}}
+template<int ...N> int bad12() { return (... N); } // expected-error {{expected expression}}