introduced pos+pos = sum_of_pos

src/typed-geometry/detail/operators/ops_pos.hh

@@ -2,6 +2,7 @@
 
 #include <typed-geometry/detail/macros.hh>
 #include <typed-geometry/detail/scalar_traits.hh>
+#include <typed-geometry/detail/sum_of_pos.hh>
 #include <typed-geometry/types/dir.hh>
 #include <typed-geometry/types/pos.hh>
 #include <typed-geometry/types/size.hh>
@@ -35,11 +36,13 @@ TG_IMPL_DEFINE_BINARY_OP_SCALAR(pos, +);
 TG_IMPL_DEFINE_BINARY_OP_SCALAR(pos, *);
 TG_IMPL_DEFINE_BINARY_OP_SCALAR_DIV(pos);
 
-// deprecated / not supported operations
+// special pos+pos handling
 template <int D, class ScalarT>
-[[deprecated("pos + pos is not a proper operation. did you mean pos + vec?")]] pos<D, ScalarT> operator+(pos<D, ScalarT> const& a, pos<D, ScalarT> const& b)
+TG_NODISCARD constexpr sum_of_pos<D, ScalarT> operator+(pos<D, ScalarT> const& a, pos<D, ScalarT> const& b)
 {
-    return a + vec(b);
+    return sum_of_pos(a) + b;
 }
 
+// deprecated / not supported operations
+
 } // namespace tg

src/typed-geometry/detail/sum_of_pos.hh

+#pragma once
+
+#include <typed-geometry/types/pos.hh>
+#include <typed-geometry/types/vec.hh>
+
+namespace tg
+{
+/*
+ * sum_of_pos is a helper struct for guaranteeing syntactic soundness when dealing with sums of positions
+ * it is the result of operator+(pos, pos)
+ * it can only be added onto other sum_of_pos
+ * to get back to a pos one needs to use operator/(sum_of_pos, ScalarT)
+ */
+template <int D, class ScalarT>
+struct sum_of_pos
+{
+    using scalar_t = ScalarT;
+    using div_t = decltype(ScalarT() / 0.0f);
+    using pos_t = pos<D, ScalarT>;
+
+    constexpr sum_of_pos() = default;
+    /* implicit */ constexpr sum_of_pos(pos_t const& p) : accum(p) {}
+
+    constexpr pos<D, div_t> operator/(div_t const& rhs) const { return accum / rhs; }
+
+    constexpr sum_of_pos operator+(sum_of_pos const& rhs) const { return accum + vec(rhs); }
+    constexpr sum_of_pos operator+(pos_t const& rhs) const { return accum + vec(rhs); }
+
+private:
+    pos_t accum;
+};
+}