cli: support for PCCVector3<T> types

Define po-lite option traits to handle PCCVector3<T> as a container
to permit using PCCVector3<T> types as command / config parameters.

tmc3/PCCMath.h

@@ -51,6 +51,12 @@ namespace pcc {
 template<typename T>
 class PCCVector3 {
 public:
+  T* begin() { return &data[0]; }
+  const T* begin() const { return &data[0]; }
+
+  T* end() { return &data[3]; }
+  const T* end() const { return &data[3]; }
+
   T& operator[](size_t i)
   {
     assert(i < 3);

tmc3/TMC3.cpp

@@ -154,6 +154,23 @@ operator<<(std::ostream& out, const AttributeEncoding& val)
 }
 }  // namespace pcc
 
+namespace df {
+namespace program_options_lite {
+  template<typename T>
+  struct option_detail<pcc::PCCVector3<T>> {
+    static constexpr bool is_container = true;
+    static constexpr bool is_fixed_size = true;
+    typedef T* output_iterator;
+
+    static void clear(pcc::PCCVector3<T>& container){};
+    static output_iterator make_output_iterator(pcc::PCCVector3<T>& container)
+    {
+      return &container[0];
+    }
+  };
+}  // namespace program_options_lite
+}  // namespace df
+
 //---------------------------------------------------------------------------
 // :: Command line / config parsing