Mesh attributes for types with memory allocation

[sebmestrallet]

I saw in the wiki of mesh attributes:

advanced In addition, arbitrary types can be used (including classes that do memory allocation). Before using a new attribute type, one needs to declare it (only once, at initialization), using geo_register_attribute_type<type>("name") (see geogram/common.cpp for example).

So I tried to add :

// ...
#include <geogram/basic/memory.h>
// ...
geo_register_attribute_type<GEO::vector<index_t>>("indices_vector");
// ...

to common.cpp, but I got:

...
geogram/basic/string.h:334:24: error: no match for ‘operator>>’ (operand types are ‘std::istringstream’ {aka ‘std::__cxx11::basic_istringstream<char>’} and ‘GEO::vector<unsigned int>’)
  334 |             return (in >> value) && (in.eof() || ((in >> std::ws) && in.eof()));
      |                    ~~~~^~~~~~~~~
...
geogram/basic/string.h:244:17: error: no match for ‘operator<<’ (operand types are ‘std::ostringstream’ {aka ‘std::__cxx11::basic_ostringstream<char>’} and ‘const GEO::vector<unsigned int>’)
  244 |             out << value;
      |             ~~~~^~~~~~~~
...

Are attributes for custom types with memory allocation still supported?

Is the compilation error related to file I/O? If so, what are the specifications for serialization of custom type attributes?

[BrunoLevy]

Hello, I confirm that attributes for types that are not POD (Plain Ordinary Datatype) is not supported.

It used to be supported in the past, but it introduces much complexity in the system, and significant runtime cost, so we decided to remove it.

One possibility is to store indices in the attribute, and store the std::strings in a vector elsewhere.

I fixed the sentence in the documentation

[sebmestrallet]

Thanks for the answer. Indeed I imagine the induced complexity.

[BrunoLevy]

Yes, it requires quite complicated machinery under the hood. It can be reactivated if there is an absolute need, but I prefer to keep the system as simple as possible (and it is already much more complicated than I wished).