Idea: use constexpr for int version functions

[ankane]

What language and solver does this apply to? C++

Describe the problem you are trying to solve.

Hi, I'd like to check the OR-Tools version during compilation to make sure it's compatible with the C++ code that uses it.

Describe the solution you'd like

Use constexpr for int version functions

constexpr int OrToolsMajorVersion();

constexpr int OrToolsMinorVersion();

constexpr int OrToolsPatchVersion();

so users can do

static_assert(
  operations_research::OrToolsMajorVersion() == 9 &&
  operations_research::OrToolsMinorVersion() == 3,
  "Incompatible OR-Tools version"
);

Describe alternatives you've considered

Another option would be to export the OR_TOOLS_MAJOR, OR_TOOLS_MINOR, and OR_TOOLS_PATCH constants.

[lperron]

not trivial.

constexpr int OrToolsMajorVersion() in the .h, defined in the .cc does not work.
in C++ 17, constexpr implies inline.

This means that the OR_TOOLS_VERSION must be used in the .h, which will not work as this will not be defined in users makefile including ortools/base/version.h

[Mizux]

I would like to use #cmakedefine since it would exactly fix this issue BUT we also need to support the bazel build -_-;
ref: https://cmake.org/cmake/help/latest/command/configure_file.html#example

[ankane]

Thanks for the responses. If it's non-trivial, no worries.

fwiw, it looks like PyTorch uses a separate script with a note about Bazel that populates version.h.in.

EDIT(mizux): and the bazel wrapper around the python script:
pytorch/pytorch:BUILD.bazel#L1625-L1637

[lperron]

Interesting link: https://dev.to/davidb31/experimentations-on-bazel-version-txt-g1k