types/description: add arity and alignment variables

CMakeLists.txt

@@ -656,6 +656,7 @@ if (TESTS)
         tuple/value
         tuple/type
         typeidx
+        types/description
         types/tagged
         uri
         utf8

test/types/description.cpp

@@ -0,0 +1,22 @@
+#include "tap.hpp"
+#include "types/description.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+int main ()
+{
+    cruft::TAP::logger tap;
+
+    tap.expect_eq (
+        cruft::types::make_description<int> (),
+        cruft::types::description {
+            .category  = cruft::types::category::SIGNED,
+            .width     = sizeof (int),
+            .arity     = 1,
+            .alignment = alignof (int)
+        },
+        "description: int"
+    );
+
+    return tap.status ();
+}

types/description.cpp

@@ -30,5 +30,9 @@ cruft::types::operator<< (std::ostream &os, cruft::types::category val)
 std::ostream&
 cruft::types::operator<< (std::ostream &os, cruft::types::description val)
 {
-    return os << "{ category: " << val.category << ", width: " << val.width << " }";
+    return os << "{ category: "  << val.category
+              << ", width: "     << val.width
+              << ", arity: "     << val.arity
+              << ", alignment: " << val.alignment
+              << " }";
 }

types/description.hpp

@@ -19,7 +19,36 @@
 
 
 namespace cruft::types {
+    ///////////////////////////////////////////////////////////////////////////
+    /// Computes the number of elements of a scalar (ie, 1), or of  statically
+    /// sized vector type
+    template <typename T, typename = void>
+    struct arity_trait { };
+
+
     //-------------------------------------------------------------------------
+    // void arity is explicitly zero.
+    template <>
+    struct arity_trait<void, void> : public std::integer_sequence<std::size_t, 0> { };
+
+
+    //-------------------------------------------------------------------------
+    // All basic types are unit arity (except for void which is zero).
+    template <typename T>
+    struct arity_trait<
+        T,
+        std::enable_if_t<std::is_fundamental_v<T>>
+    > : public std::integral_constant<
+        std::size_t, 1u
+    > { };
+
+
+    //-------------------------------------------------------------------------
+    template <typename T>
+    constexpr auto arity_v = arity_trait<T>::value;
+
+
+    ///////////////////////////////////////////////////////////////////////////
     enum class category {
         NONE,
         UNSIGNED,
@@ -27,20 +56,36 @@ namespace cruft::types {
         REAL,
     };
 
-    //-------------------------------------------------------------------------
+
+    ///------------------------------------------------------------------------
+    /// A description of the type that makes up a scalar or vector type.
+    ///
+    /// A vector3f would be { REAL, sizeof(float), 3 };
     struct description {
         /// The signed, realness, or voidness of the type.
         enum category category;
 
         /// The number of bytes for an individual instance of this type.
         std::size_t width;
+
+        /// The number of variables that make up an instance.
+        std::size_t arity;
+
+        std::size_t alignment;
+
+        /// Returns the number of bytes required to store this type.
+        constexpr std::size_t size (void) const noexcept { return width * arity; }
     };
 
+
+    //-------------------------------------------------------------------------
     constexpr bool
     operator== (description const &a, description const &b) noexcept
     {
-        return a.category == b.category &&
-               a.width    == b.width;
+        return a.category  == b.category &&
+               a.width     == b.width    &&
+               a.arity     == b.arity    &&
+               a.alignment == b.alignment;
     }
 
 
@@ -72,13 +117,17 @@ namespace cruft::types {
     {
         if constexpr (std::is_void_v<T>) {
             return {
-                .category = category::NONE,
-                .width    = 0,
+                .category  = category::NONE,
+                .width     = 0,
+                .arity     = 1,
+                .alignment = 0,
             };
         } else {
             return {
                 .category = category_traits_v<T>,
-                .width = sizeof (T)
+                .width = sizeof (T),
+                .arity = arity_v<T>,
+                .alignment = alignof (T)
             };
         }
     }