Subscript operator for iterables and tests for constexpr iterators.

enum.h

@@ -346,6 +346,8 @@ struct _Iterable {
     constexpr iterator begin() const { return iterator(_array); }
     constexpr iterator end() const { return iterator(_array + _size); }
     constexpr size_t size() const { return _size; }
+    constexpr const Element& operator [](size_t index) const
+        { return _array[index]; }
 
     constexpr _Iterable(const Element *array, size_t size) :
         _array(array), _size(size) { };

example/4-constexpr.cc

@@ -33,6 +33,7 @@ constexpr bool          should_be_invalid_3 = Channel::_is_valid_nocase("reed");
 // _names and _values collections and iterators.
 constexpr Channel       channel_5 = *(Channel::_values.begin() + 1);
 constexpr const char    *name_through_iterator = *(Channel::_names.begin() + 1);
+constexpr const char    *name_through_subscript = Channel::_names[2];
 
 // Range properties.
 constexpr Channel       channel_6 = Channel::_max;
@@ -89,6 +90,8 @@ int main()
     std::cout << "constexpr trimmed name: " << channel_1_name << std::endl;
     std::cout << "constexpr name through iterator: "
               << name_through_iterator << std::endl;
+    std::cout << "constexpr name through suscript: "
+              << name_through_subscript << std::endl;
     std::cout << "span: " << span << std::endl;
     std::cout << "type name: " << name << std::endl;
 

example/8-constexpr-iterate.cc

@@ -0,0 +1,81 @@
+// Compile-time iteration. This example generates an approximation of enum
+// declarations (without explicit "="" settings) at run time. The storage space
+// for this is reserved at compile time, however.
+
+#include <cassert>
+#include <cstring>
+#include <iostream>
+#include <enum.h>
+
+ENUM(Channel, int, Red, Green, Blue);
+ENUM(Depth, int, TrueColor, HighColor);
+
+// Computes the length of a string.
+constexpr size_t string_length(const char *s, size_t index = 0)
+{
+    return s[index] == '\0' ? index : string_length(s, index + 1);
+}
+
+// Runs over all the constants in an enum and adds up the lengths of their
+// names.
+template <typename Enum>
+constexpr size_t total_names_length(size_t accumulator = 0, size_t index = 0)
+{
+    return
+        index == Enum::_size ? accumulator :
+        total_names_length<Enum>
+            (accumulator + string_length(Enum::_names[index]), index + 1);
+}
+
+// Computes the total length of an ENUM declaration, assuming the type is int.
+// The summands correspond to each of the tokens and spaces (i.e., "ENUM", "(",
+// etc.). (Enum::_size - 1) * 2 is added to account for each comma and space
+// following each constant name, except for the last one. The final 1 is added
+// to account for the null terminator.
+template <typename Enum>
+constexpr size_t declaration_length()
+{
+    return
+        4 + 1 + string_length(Enum::_name) + 1 + 1 + 3 + 1 + 1 +
+        total_names_length<Enum>() + (Enum::_size - 1) * 2 + 1 + 1 + 1;
+}
+
+// Formats the declaration into space already reserved.
+template <typename Enum>
+void format_declaration(char *storage)
+{
+    std::strcat(storage, "ENUM(");
+    std::strcat(storage, Enum::_name);
+    std::strcat(storage, ", int, ");
+
+    for (auto name_iterator = Enum::_names.begin();
+         name_iterator < Enum::_names.end() - 1; ++name_iterator) {
+
+        std::strcat(storage, *name_iterator);
+        std::strcat(storage, ", ");
+    }
+    std::strcat(storage, (+Enum::_last).to_string());
+
+    std::strcat(storage, ");");
+
+    assert(std::strlen(storage) == declaration_length<Enum>() - 1);
+}
+
+// Reserve space for the formatted declaration of each enum. These buffers
+// should be zeroed at load time or during code generation, so, semantically,
+// they contain the empty string.
+char    channel_declaration[declaration_length<Channel>()];
+char    depth_declaration[declaration_length<Depth>()];
+
+
+
+int main()
+{
+    format_declaration<Channel>(channel_declaration);
+    std::cout << channel_declaration << std::endl;
+
+    format_declaration<Depth>(depth_declaration);
+    std::cout << depth_declaration << std::endl;
+
+    return 0;
+}

test/cxxtest/tests.h

@@ -128,7 +128,13 @@ static_assert_1(!Channel::_is_valid_nocase("greeen"));
 // Iterables.
 static_assert_1(Channel::_values.size() == Channel::_size);
 static_assert_1(*Channel::_values.begin() == Channel::_first);
+static_assert_1(*(Channel::_values.begin() + 1) == Channel::Green);
+static_assert_1(*(Channel::_values.begin() + 2) == Channel::Blue);
+static_assert_1(Channel::_values[1] == Channel::Green);
+static_assert_1(Channel::_values[2] == Channel::Blue);
 static_assert_1(Channel::_names.size() == Channel::_size);
+// The next one is a little janky, but actually the pointers should be the same.
+static_assert_1(*Channel::_names.begin() == (+Channel::_first).to_string());
 
 
 
@@ -149,7 +155,8 @@ class EnumTests : public CxxTest::TestSuite {
     void test_string_conversions()
     {
         TS_ASSERT_EQUALS(strcmp((+Channel::Green).to_string(), "Green"), 0);
-        TS_ASSERT_EQUALS(strcmp((+Channel::Blue).to_string(), "Blue"), 0);
+        TS_ASSERT_EQUALS(strcmp((+Depth::HighColor).to_string(),
+                         "HighColor"), 0);
 
         TS_ASSERT_THROWS(Channel::_from_string("green"), std::runtime_error);
         TS_ASSERT_THROWS(Channel::_from_string_nocase("a"), std::runtime_error);