add factory function with forced type

src/field.h

@@ -260,6 +260,7 @@ public:
 
   static Field_t init(const CdoVar &var);
   static Field_t init(const MemType memType);
+  static Field_t init(const CdoVar &var, const MemType memType);
 
   static Field3D_t init3D(const CdoVar &var);
   static Field3D_t init3D(const MemType memType);

src/field_factory.inl

@@ -29,6 +29,16 @@ inline Field_t FieldFactory::init(const MemType memType) {
   }
 }
 
+inline Field_t FieldFactory::init(const CdoVar& var, const MemType memType) {
+  if(memType == MemType::Float) {
+    return Field<float>{var.gridID, var.gridsize, var.missval, var.gridsize * var.nwpv};
+  } else if (memType == MemType::Double) {
+    return Field<double>{var.gridID, var.gridsize, var.missval, var.gridsize * var.nwpv};
+  } else {
+    throw std::runtime_error("Not supported type");
+  }
+}
+
 inline Field3D_t FieldFactory::init3D(const CdoVar& var) {
   if(var.memType == MemType::Float) {
     return Field3D<float>{var.gridID, var.gridsize, var.missval, var.gridsize * var.nwpv, var.nlevels};