Math: add an ability to construct a Range1D from Math::Vector<1, T>.

A Vector<1, T> is implicitly constructible from T but not vice versa (to
avoid nasty collisions with builtin operators on scalars) so this is
needed.

src/Magnum/Math/Range.h

@@ -37,9 +37,24 @@ namespace Magnum { namespace Math {
 namespace Implementation {
     template<UnsignedInt, class> struct RangeTraits;
 
-    template<class T> struct RangeTraits<1, T> { typedef T Type; };
-    template<class T> struct RangeTraits<2, T> { typedef Vector2<T> Type; };
-    template<class T> struct RangeTraits<3, T> { typedef Vector3<T> Type; };
+    template<class T> struct RangeTraits<1, T> {
+        typedef T Type;
+        constexpr static Type fromVector(const Vector<1, T>& value) {
+            return value[0];
+        }
+    };
+    template<class T> struct RangeTraits<2, T> {
+        typedef Vector2<T> Type;
+        constexpr static Type fromVector(const Vector<2, T>& value) {
+            return value;
+        }
+    };
+    template<class T> struct RangeTraits<3, T> {
+        typedef Vector3<T> Type;
+        constexpr static Type fromVector(const Vector<3, T>& value) {
+            return value;
+        }
+    };
 
     template<UnsignedInt, class, class> struct RangeConverter;
 }
@@ -117,6 +132,11 @@ template<UnsignedInt dimensions, class T> class Range {
 
         /** @brief Construct a range from minimal and maximal coordinates */
         constexpr /*implicit*/ Range(const VectorType& min, const VectorType& max) noexcept: _min{min}, _max{max} {}
+        /** @overload */
+        #ifndef DOXYGEN_GENERATING_OUTPUT
+        template<UnsignedInt d = dimensions, class = typename std::enable_if<d == 1>::type>
+        #endif
+        constexpr /*implicit*/ Range(const Vector<dimensions, T>& min, const Vector<dimensions, T>& max) noexcept: _min{Implementation::RangeTraits<dimensions, T>::fromVector(min)}, _max{Implementation::RangeTraits<dimensions, T>::fromVector(max)} {}
 
         /**
          * @brief Construct a range from a pair of minimal and maximal coordinates

src/Magnum/Math/Test/RangeTest.cpp

@@ -101,6 +101,7 @@ struct RangeTest: Corrade::TestSuite::Tester {
     explicit RangeTest();
 
     void construct();
+    void construct1DFromVectors();
     void constructDefault();
     void constructNoInit();
     void constructFromSize();
@@ -156,6 +157,7 @@ typedef Vector3<Int> Vector3i;
 
 RangeTest::RangeTest() {
     addTests({&RangeTest::construct,
+              &RangeTest::construct1DFromVectors,
               &RangeTest::constructDefault,
               &RangeTest::constructNoInit,
               &RangeTest::constructFromSize,
@@ -211,6 +213,17 @@ void RangeTest::construct() {
     CORRADE_VERIFY(std::is_nothrow_constructible<Range3Di, Vector3i, Vector3i>::value);
 }
 
+void RangeTest::construct1DFromVectors() {
+    /* Used by EigenIntegration for Range3D conversion. Implementing the same
+       there would be a massive verbose pain and this could be useful elsewhere
+       as well, so implementing that directly on a Range. */
+    constexpr Range1Di a = {Vector<1, Int>{3}, Vector<1, Int>{23}};
+
+    CORRADE_COMPARE(a, (Range<1, Int>(3, 23)));
+
+    CORRADE_VERIFY(std::is_nothrow_constructible<Range1Di, Vector<1, Int>, Vector<1, Int>>::value);
+}
+
 void RangeTest::constructDefault() {
     constexpr Range1Di a1;
     constexpr Range2Di b1;