diff --git a/detail/coord.hpp b/detail/coord.hpp
index 16d78888..8f051fe7 100644
--- a/detail/coord.hpp
+++ b/detail/coord.hpp
@@ -209,6 +209,8 @@ namespace util {
             using coord_init<S,T,tags...>::coord_init;
             coord () = default;
 
+            size_t size (void) const { return S; }
+
             explicit coord (T v)
             { std::fill (std::begin (this->data), std::end (this->data), v); }
 
diff --git a/extent.cpp b/extent.cpp
index ec44ed43..28b78d96 100644
--- a/extent.cpp
+++ b/extent.cpp
@@ -24,59 +24,27 @@
 
 #include <cmath>
 
+
 ///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
-util::extent<S,T>::extent (const T  _width, const T  _height):
-        w (_width),
-        h (_height)
-{
-    static_assert (S == 2, "extents currently only support 2 dimensions");
-
-    CHECK_GE (w, 0);
-    CHECK_GE (h, 0);
-}
-
-
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
-util::extent<S,T>::extent (T t):
-    extent (t, t)
-{ ; }
-
-
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
 util::extent<S,T>::extent (vector<S,T> _v):
     extent (_v.x, _v.y)
 { ; }
 
 
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
-util::extent<S,T>::extent (const util::extent<S,T> &rhs):
-        w (rhs.w),
-        h (rhs.h)
-{ ; }
-
-
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
-util::extent<S,T>&
-util::extent<S,T>::operator= (extent<S,T> rhs)
-{
-    w = rhs.w;
-    h = rhs.h;
-
-    return *this;
-}
-
-
 ///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
 T
 util::extent<S,T>::diameter (void) const
 {
-    return static_cast<T> (sqrt (w * w + h * h));
+    return static_cast<T> (
+        std::sqrt (
+            std::accumulate (std::begin (this->data),
+                             std::end   (this->data),
+                             T {0},
+                             [] (auto a, auto b) { return a + b * b; })
+        )
+    );
 }
 
 
@@ -85,7 +53,10 @@ template <size_t S, typename T>
 T
 util::extent<S,T>::area (void) const
 {
-    return w * h;
+    return std::accumulate (std::begin (this->data),
+                            std::end   (this->data),
+                            T {1},
+                            std::multiplies<T> ());
 }
 
 
@@ -94,10 +65,7 @@ template <size_t S, typename T>
 util::extent<S,T>
 util::extent<S,T>::expanded (util::vector<S,T> mag) const
 {
-    return {
-        w + mag.x,
-        h + mag.y
-    };
+    return *this + mag;
 }
 
 
@@ -110,15 +78,6 @@ util::extent<S,T>::expanded (T t) const
 }
 
 
-///////////////////////////////////////////////////////////////////////////////
-template <size_t S, typename T>
-float
-util::extent<S,T>::aspect (void) const
-{
-    return static_cast<float> (w) / static_cast<float> (h);
-}
-
-
 ///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
 bool
@@ -130,40 +89,15 @@ util::extent<S,T>::empty (void) const
 
 ///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
-T&
-util::extent<S,T>::operator[] (size_t idx)
+util::extent<S,T>
+util::extent<S,T>::operator+ (vector<S,T> rhs) const
 {
-    switch (idx) {
-    case 0: return w;
-    case 1: return h;
-
-    default:
-        unreachable ();
-    }
-}
-
-
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
-const T&
-util::extent<S,T>::operator[] (size_t idx) const
-{
-    switch (idx) {
-    case 0: return w;
-    case 1: return h;
-
-    default:
-        unreachable ();
-    }
-}
-
-
-//-----------------------------------------------------------------------------
-template <size_t S, typename T>
-size_t
-util::extent<S,T>::size (void) const
-{
-    return S;
+    extent<S,T> out;
+    std::adjacent_difference (std::begin (this->data),
+                              std::end   (this->data),
+                              std::begin (rhs.data),
+                              std::plus<T> ());
+    return out;
 }
 
 
@@ -172,22 +106,21 @@ template <size_t S, typename T>
 bool
 util::extent<S,T>::operator ==(const extent& rhs) const
 {
-    return almost_equal (w, rhs.w) &&
-           almost_equal (h, rhs.h);
+    return std::equal (std::begin (this->data),
+                       std::end   (this->data),
+                       std::begin (rhs.data),
+                       almost_equal<T>);
 }
 
 
 ///////////////////////////////////////////////////////////////////////////////
 template <size_t S, typename T>
-const util::extent<S,T> util::extent<S,T>::MIN {
-    0, 0
-};
+const util::extent<S,T> util::extent<S,T>::MIN { 0 };
 
 
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
 const util::extent<S,T> util::extent<S,T>::MAX {
-    std::numeric_limits<T>::max (),
     std::numeric_limits<T>::max ()
 };
 
diff --git a/extent.hpp b/extent.hpp
index 0eee6111..1409ada5 100644
--- a/extent.hpp
+++ b/extent.hpp
@@ -20,8 +20,8 @@
 #ifndef __UTIL_EXTENT_HPP
 #define __UTIL_EXTENT_HPP
 
+#include "detail/coord.hpp"
 #include "vector.hpp"
-
 #include <iostream>
 
 
@@ -30,15 +30,10 @@ namespace util {
      * A pure two-dimensional size, without positioning
      */
     template <size_t S, typename T>
-    struct extent {
-        T w, h;
-
-        extent (const T  _width, const T  _height);
-        extent (T);
-        extent (vector<S,T>);
-        extent (const extent&);
-        extent& operator= (extent);
+    struct extent : public detail::coord<S,T,detail::whd> {
+        using detail::coord<S,T,detail::whd>::coord;
         extent () = default;
+        extent (vector<S,T>);
 
         T    area  (void) const;
         T diameter (void) const;
@@ -46,14 +41,9 @@ namespace util {
         extent expanded (vector<S,T>) const;
         extent expanded (T) const;
 
-        float aspect (void) const;
-
         bool empty (void) const;
 
-        T& operator[] (size_t idx);
-        const T& operator[] (size_t idx) const;
-
-        size_t size (void) const;
+        extent<S,T> operator+ (vector<S,T>) const;
 
         bool operator ==(const extent& rhs) const;
         bool operator !=(const extent& rhs) const
@@ -66,6 +56,10 @@ namespace util {
         static const extent MIN;
     };
 
+    template <typename U, typename T>
+    U
+    aspect (extent<2,T>);
+
     typedef extent<2,int> extent2i;
     typedef extent<2,size_t> extent2u;
     typedef extent<2,float> extent2f;
diff --git a/extent.ipp b/extent.ipp
index b01f5cd3..b7d12a05 100644
--- a/extent.ipp
+++ b/extent.ipp
@@ -19,19 +19,29 @@
 
 
 #ifdef __UTIL_EXTENT_IPP
-#error "twice included ipp"
+#error
 #endif
 
 #define __UTIL_EXTENT_IPP
 
+#include <algorithm>
+
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
 template <typename U>
 util::extent<S,U>
 util::extent<S,T>::cast (void) const
 {
-    return {
-        static_cast<U> (w),
-        static_cast<U> (h)
-    };
+    util::extent<S,U> out;
+    std::copy (std::begin (this->data), std::end (this->data), std::begin (out.data));
+    return out;
+}
+
+
+//-----------------------------------------------------------------------------
+template <typename U, typename T>
+U
+util::aspect (util::extent<2,T> e)
+{
+    return static_cast<U> (e.w) / e.h;
 }
diff --git a/region.cpp b/region.cpp
index a30f37c1..c72cf0c0 100644
--- a/region.cpp
+++ b/region.cpp
@@ -37,7 +37,7 @@ util::region<S,T>::region (extent_t _extent):
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
 util::region<S,T>::region (point_t _point,
-                         extent_t _size):
+                           extent_t _size):
     x (_point.x),
     y (_point.y),
     w (_size.w),
@@ -48,7 +48,7 @@ util::region<S,T>::region (point_t _point,
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
 util::region<S,T>::region (point_t _a,
-                         point_t _b):
+                           point_t _b):
     region (_a, _b - _a)
 {
     CHECK_GE (_b.x, _a.x);