Merge pull request #128 from daniel-j-h/match

Pattern Matching for Sum Types via `.match` Member Function
mapbox · Nov 21, 2016 · ed84def · ed84def
2 parents 3c17c37 + 720c237
commit ed84def
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Showing 3 changed files with 58 additions and 4 deletions.
diff --git a/include/mapbox/variant.hpp b/include/mapbox/variant.hpp
@@ -13,6 +13,7 @@
 #include <functional>
 
 #include <mapbox/recursive_wrapper.hpp>
+#include <mapbox/variant_visitor.hpp>
 
 // clang-format off
 // [[deprecated]] is only available in C++14, use this for the time being
@@ -872,6 +873,22 @@ class variant
         return detail::binary_dispatcher<F, V, R, Types...>::apply(v0, v1, std::forward<F>(f));
     }
 
+    // match
+    // unary
+    template <typename... Fs>
+    auto VARIANT_INLINE match(Fs&&... fs) const
+        -> decltype(variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...)))
+    {
+        return variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...));
+    }
+    // non-const
+    template <typename... Fs>
+    auto VARIANT_INLINE match(Fs&&... fs)
+        -> decltype(variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...)))
+    {
+        return variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...));
+    }
+
     ~variant() noexcept // no-throw destructor
     {
         helper_type::destroy(type_index, &data);

diff --git a/include/mapbox/variant_visitor.hpp b/include/mapbox/variant_visitor.hpp
@@ -10,6 +10,7 @@ struct visitor;
 template <typename Fn>
 struct visitor<Fn> : Fn
 {
+    using type = Fn;
     using Fn::operator();
 
     visitor(Fn fn) : Fn(fn) {}
@@ -18,6 +19,7 @@ struct visitor<Fn> : Fn
 template <typename Fn, typename... Fns>
 struct visitor<Fn, Fns...> : Fn, visitor<Fns...>
 {
+    using type = visitor;
     using Fn::operator();
     using visitor<Fns...>::operator();
 

diff --git a/test/lambda_overload_test.cpp b/test/lambda_overload_test.cpp
@@ -55,8 +55,8 @@ void test_singleton_variant()
     apply_visitor(make_visitor([](int) {}), singleton);
 }
 
-#ifdef HAS_CPP14_SUPPORT
 void test_lambda_overloads_sfinae()
+#ifdef HAS_CPP14_SUPPORT
 {
     variant<int, float, std::vector<int>> var;
 
@@ -76,17 +76,52 @@ void test_lambda_overloads_sfinae()
     var = std::vector<int>{4, 5, 6};
     apply_visitor(visitor, var);
 }
+#else
+{
+}
 #endif
 
+void test_match_singleton()
+{
+    variant<int> singleton = 5;
+    singleton.match([](int) {});
+}
+
+void test_match_overloads()
+{
+    Either<Error, Response> rv;
+
+    rv = Response{};
+
+    rv.match([](Response) { std::cout << "Response\n"; }, //
+             [](Error) { std::cout << "Error\n"; });      //
+}
+
+void test_match_overloads_capture()
+{
+    Either<Error, Response> rv;
+
+    rv = Error{};
+
+    int ok = 0;
+    int err = 0;
+
+    rv.match([&](Response) { ok += 1; }, //
+             [&](Error) { err += 1; });  //
+
+    std::cout << "Got " << ok << " ok, " << err << " err" << std::endl;
+}
+
 int main()
 {
     test_lambda_overloads();
     test_singleton_variant();
     test_lambda_overloads_capture();
-
-#ifdef HAS_CPP14_SUPPORT
     test_lambda_overloads_sfinae();
-#endif
+
+    test_match_singleton();
+    test_match_overloads();
+    test_match_overloads_capture();
 }
 
 #undef HAS_CPP14_SUPPORT