Fix subscript return types.

alialib · Aug 8, 2018 · aaf983a · aaf983a
1 parent b9cc52d
commit aaf983a
Show file tree

Hide file tree

Showing 2 changed files with 62 additions and 47 deletions.
diff --git a/src/alia/signals/operators.hpp b/src/alia/signals/operators.hpp
@@ -377,28 +377,13 @@ struct has_at_indexer<
 {
 };
 
-// has_const_subscript<Container, Index>::value yields a compile-time boolean
-// indicating whether or not Container has a const subscript operator that takes
-// an Index.
-template<class Container, class Index, class = void_t<>>
-struct has_const_subscript : std::false_type
-{
-};
-template<class Container, class Index>
-struct has_const_subscript<
-    Container,
-    Index,
-    void_t<decltype(std::declval<Container const&>()[std::declval<Index>()])>>
-    : std::true_type
-{
-};
-
 template<class Container, class Index>
 auto
 invoke_const_subscript(
     Container const& container,
     Index const& index,
-    std::enable_if_t<has_const_subscript<Container, Index>::value>* = 0)
+    std::enable_if_t<!has_at_indexer<Container, Index>::value>* = 0)
+    -> decltype(container[index])
 {
     return container[index];
 }
@@ -408,9 +393,8 @@ auto
 invoke_const_subscript(
     Container const& container,
     Index const& index,
-    std::enable_if_t<
-        !has_const_subscript<Container, Index>::value
-        && has_at_indexer<Container, Index>::value>* = 0)
+    std::enable_if_t<has_at_indexer<Container, Index>::value>* = 0)
+    -> decltype(container.at(index))
 {
     return container.at(index);
 }

diff --git a/unit_tests/signals/operators.cpp b/unit_tests/signals/operators.cpp
@@ -228,6 +228,59 @@ TEST_CASE("field signal", "[signals]")
     REQUIRE(f.y == 0.5);
 }
 
+struct my_array
+{
+    int x[3] = {1, 2, 3};
+    int& operator[](int i)
+    {
+        return x[i];
+    }
+    int const& operator[](int i) const
+    {
+        return x[i];
+    }
+};
+
+struct my_const_array
+{
+    int x[3] = {1, 2, 3};
+    int operator[](int i) const
+    {
+        return x[i];
+    }
+};
+
+// Test some of the helper metafunctions for subscript signals.
+TEST_CASE("subscript metafunctions", "[signals]")
+{
+    REQUIRE(has_at_indexer<std::vector<int>, int>::value);
+    REQUIRE(has_at_indexer<std::map<int, int>, int>::value);
+    REQUIRE(has_at_indexer<std::vector<bool>, int>::value);
+    REQUIRE(!has_at_indexer<my_array, int>::value);
+    REQUIRE(!has_at_indexer<my_const_array, int>::value);
+
+    REQUIRE((std::is_same<
+             subscript_result_type<std::vector<float>, int>::type,
+             float>::value));
+    REQUIRE((std::is_same<
+             subscript_result_type<std::map<int, float>, int>::type,
+             float>::value));
+    REQUIRE((std::is_same<
+             subscript_result_type<std::vector<bool>, int>::type,
+             bool>::value));
+    REQUIRE(
+        (std::is_same<subscript_result_type<my_array, int>::type, int>::value));
+    REQUIRE(
+        (std::is_same<subscript_result_type<my_const_array, int>::type, int>::
+             value));
+
+    REQUIRE(const_subscript_returns_reference<std::vector<int>, int>::value);
+    REQUIRE(const_subscript_returns_reference<std::map<int, int>, int>::value);
+    REQUIRE(!const_subscript_returns_reference<std::vector<bool>, int>::value);
+    REQUIRE(const_subscript_returns_reference<my_array, int>::value);
+    REQUIRE(!const_subscript_returns_reference<my_const_array, int>::value);
+}
+
 TEST_CASE("vector subscript", "[signals]")
 {
     using namespace alia;
@@ -255,8 +308,8 @@ TEST_CASE("vector subscript", "[signals]")
     write_signal(s, 1);
     REQUIRE(c == std::vector<int>({2, 1, 3}));
 
-    // Check that changes in the container and the index both cause changes in
-    // the value ID.
+    // Check that changes in the container and the index both cause changes
+    // in the value ID.
     REQUIRE(!original_id.matches(s.value_id()));
     auto t = c_signal[value(0)];
     REQUIRE(t.value_id() != s.value_id());
@@ -340,25 +393,12 @@ TEST_CASE("map subscript", "[signals]")
 
 TEST_CASE("custom ref subscript", "[signals]")
 {
-    struct my_vector
-    {
-        int x[3] = {1, 2, 3};
-        int& operator[](int i)
-        {
-            return x[i];
-        }
-        int const& operator[](int i) const
-        {
-            return x[i];
-        }
-    };
-
-    my_vector c;
+    my_array c;
     auto c_signal = lambda_bidirectional(
         always_readable,
         [&]() { return c; },
         always_writable,
-        [&](my_vector const& v) { c = v; },
+        [&](my_array const& v) { c = v; },
         [&]() {
             return unit_id; // doesn't really matter
         });
@@ -378,16 +418,7 @@ TEST_CASE("custom ref subscript", "[signals]")
 
 TEST_CASE("custom by-value subscript", "[signals]")
 {
-    struct my_vector
-    {
-        int x[3] = {1, 2, 3};
-        int operator[](int i) const
-        {
-            return x[i];
-        }
-    };
-
-    my_vector c;
+    my_const_array c;
     auto c_signal = lambda_input(
         always_readable,
         [&]() { return c; },