Create code working for multiple platforms and versions

[mdenty]

1. Operating system I develop on macOS Sonoma and I build on Linux Ubuntu 22.04 (at the time of writing)
2. The way you installed OpenCV:
   • macOS : brew
   • Linux : apt
3. OpenCV version
   • macOS: 4.8.1_5
   • Linux: 4.5.4
4. rustc version (rustc --version)
   • macOS: 1.74.0
   • Linux: 1.70

The issue is that I code:

        let sift = <SIFT>::create(
            params.nfeatures,
            params.noctave_layers,
            params.contrast_threshold,
            params.edge_threshold,
            params.sigma,
            params.enable_precise_upscale,
        )
        .expect("SIFT");

It compiles fine on the Mac but fails on the Linux box with the error message:

error[E0061]: this function takes 5 arguments but 6 arguments were supplied

The argument enable_precise_upscale appeared in version 4.8.0.

What is the best way to cope with this problem? I do not want to do a conditional compilation OS kind, since it will probably fail when 24.04 will be out.

For today, I did what I did not want to do:

        let sift = <SIFT>::create(
            params.nfeatures,
            params.noctave_layers,
            params.contrast_threshold,
            params.edge_threshold,
            params.sigma,
            #[cfg(target_os = "macos")] 
            params.enable_precise_upscale,
        )
        .expect("SIFT");

[twistedfall]

For this particular case I think you can use SIFT::create_def_1 (automatic naming sorry ^^”). The *_def functions are the variants of regular functions but without the arguments that have a default value in C++. In general case you can also check opencv_branch_34 and friends, but that’s for major OpenCV branches.

[mdenty]

Good to know about *_def functions. I'll keep that in mind.

[mdenty]

For some reason the SIFT::create_def_1 is not found under Linux:

error[E0599]: no function or associated item named `create_def_1` found for struct `SIFT` in the current scope
   --> src/some/dir/model.rs:390:28
    |
390 |         let sift = <SIFT>::create_def_1(
    |                            ^^^^^^^^^^^^
    |                            |
    |                            function or associated item not found in `SIFT`
    |                            help: there is an associated function with a similar name: `create_def`
For more information about this error, try `rustc --explain E0599`.
error: could not compile `project` (lib) due to previous error

It compiles fine under macOS, tho.

Back to square # 1.

[twistedfall]

This happens because of automatic renaming and the way how those functions are defined between those OpenCV versions. I'll try to fix this particular issue in the next create release.

[twistedfall]

After some tries it looks like it won't really work unfortunately. The most robust solution in your case is to have matching OpenCV versions between the environments.