Merge branch 'master' of https://github.com/thepowersgang/mrustc

# Conflicts:
#	src/common.hpp
#	src/hir/deserialise.cpp
#	src/hir_typeck/static.cpp
#	src/mir/from_hir.cpp
#	src/mir/from_hir.hpp
#	src/mir/from_hir_match.cpp
#	src/mir/helpers.hpp
#	src/mir/mir_builder.cpp

1 files changed, 70 insertions, 0 deletions

diff --git a/Notes/BigChanges/Variant.md b/Notes/BigChanges/Variant.md
new file mode 100644
index 00000000..55bb3bb0
--- /dev/null
+++ b/Notes/BigChanges/Variant.md
@@ -0,0 +1,70 @@
+
+(the below is from @ubsan)
+
+```
+// one can define their own variant, but I'm lazy
+#include <variant>
+#include <type_traits>
+#include <iostream>
+
+template <typename F, typename T, typename Void = void>
+struct return_type {};
+
+template <typename F, typename T>
+struct return_type<T, F, std::void_t<
+  decltype(std::declval<F>()(std::declval<T>()))
+>> {
+  using type = decltype(std::declval<F>()(std::declval<T>()));
+};
+
+template <typename F, typename T>
+using return_type_t = typename return_type<T, F>::type;
+
+// not sure what to call this
+template <typename F, typename... Ts>
+struct common_return_type {
+  using type = std::common_type_t<return_type_t<F, Ts>...>;
+};
+
+template <typename F, typename... Ts>
+using common_return_type_t = typename common_return_type<F, Ts...>::type;
+
+template <typename F, typename... Ts>
+auto match(
+  std::variant<Ts...>& variant, F&& functor
+) -> common_return_type_t<F, Ts...> {
+  // you could also use static_assert to make it SFINAE-unfriendly
+  return std::visit(functor, variant);
+}
+
+template <typename... Fs>
+struct overloaded : Fs... {
+  using Fs::operator()...;
+  overloaded(Fs&&... fs) : Fs(std::forward<Fs>(fs))... { }
+};
+
+int main() {
+  auto var = std::variant<int, std::string>(0);
+  std::cout << match(var, overloaded(
+    [](int i) { return i; },
+    [](std::string s) { return 0; }
+  ));
+}
+```
+
+
+
+ALTERNATIVE
+===========
+
+Could just update TU to have:
+``
+stmt.if_let(
+stmt.match_def(
+stmt.match(
+    [](::MIR::LValue::Data_Assign& se) {
+    },
+    [](::MIR::LValue::Data_Drop& se) {
+    }
+    );
+```