Cargo VS opencv-rust

To create a new application we'll use cargo (a build tool and also a package manager for Rust. It is used for scaffolding new library/binary projects). So in your projects folder, you can run this command in your terminal:

> ...but at the end of the day Cargo is the reason that Rust is popular.

FWIW, maybe that's true for you, but there are numerous other advantages to the language for which many people choose to use Rust--some even "despite" Cargo: you see Google having had to put in way way WAY too much work to get Bazel working for Rust :/--that it honestly feels a bit like belittling an extremely important language to make this claim so flippantly.

> You can set a default build target for a Cargo project with two lines of configuration, no nightly features necessary...

This doesn't work as, as soon as you start setting target-specific options, it infects the host build, as they incorrectly modelled the problem as some kind of map from targets to flags. If you don't believe me, on your Linux computer, try cross-compile something complicated that will runs on a "least common denominator" Linux distribution, such as CentOS 7.

> Can you clarify what this is referring to?

Sure. I've Googled rust cargo target host bugs for you (which, FWIW, finds a number of bugs I've filed or have talked about, but it isn't as if I have a list anywhere). Note that one of these bugs is "closed", but I still provide them for context as a patch might have been merged but (as you'll find out if you read through all of these) it isn't stable.

https://github.com/rust-lang/cargo/issues/8147

https://github.com/rust-lang/cargo/issues/3349

https://github.com/rust-lang/cargo/pull/9322

https://github.com/rust-lang/cargo/issues/9453

https://github.com/rust-lang/cargo/pull/9753

The result of this work being left incomplete is that increasingly large numbers of "serious" projects--things I'd expect people in packaging land to have heard of, such as BuildRoot--are being forced to set the ridiculous environment variable __CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS="nightly" in order to get access to a flag that makes Cargo sort of work.

(And yet, I often see people surprised at how long it is taking for various of the more important clients to fully get into using Rust, as the safety issues are so severe from continuing to use C/C++: as you made the contention that you believe the reason why people use Rust is Cargo, I will say the opposite: the reason why we don't see more Rust is also Cargo.)

What has worked for me so far:

https://doc.rust-lang.org/book/

(do the exercises!)

plus a little bit of:

https://doc.rust-lang.org/cargo/

and

https://doc.rust-lang.org/std/index.html

(There's no need to remember the last URL -- just google "rust xxx" and you will get the right page.)

I'm looking forward to reading this:

https://nnethercote.github.io/perf-book/introduction.html

Sprinkle some blog posts on top:

https://xxchan.me/cs/2023/02/17/optimize-rust-comptime-en.ht...

https://matklad.github.io/2021/05/31/how-to-test.html

https://matklad.github.io/2021/08/22/large-rust-workspaces.h...

https://fasterthanli.me/articles/a-half-hour-to-learn-rust

https://fasterthanli.me/articles/working-with-strings-in-rus...

... and the rest is just a matter of applying enough sweat :)

I actually agree, yet it still has shortcomings. For eg https://github.com/rust-lang/cargo/issues/545 is still open (it's from 2014!!)

Rust uses a system to manage its libraries called Cargo. You can read more here. We can edit the Cargo.toml file and add the library under [dependencies].

From cargo's changelog [0]

> Automatically inherit workspace fields when running `cargo new`/`cargo init`. #12069 [1]

imo I think this is a big quality of life improvement

[0] https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#...

[1] https://github.com/rust-lang/cargo/pull/12069

You're probably running into this: https://github.com/rust-lang/cargo/issues/7058

`cargo vendor` will download dependencies for all platforms, which leads to a lot of unused code being pulled in. In this case, the Windows API and Microsoft compiler wrappers.

In this instance, during the build process "tempfile" is used as a dev-dependency, which has a runtime dependency on windows-sys when compiling Windows binaries. I'm not entirely sure why (commenting it out in Cargo.toml doesn't seem to break the build).

After commenting it out and manually removing the spurious Windows API files as well as the unrelated packages (ctor diff output_vt100 pretty_assertions proc-macro2 quote syn unicode-ident yansi), I get the following results:

          0.0358 secs

btw we are looking at making the resolver to automatically select compatible MSRV dependencies. See https://github.com/rust-lang/cargo/issues/9930

Looking around I found also https://github.com/rust-lang/cargo/issues/10599, so I think I'm remembering correctly. Note that that mentions public/private dependencies. Most likely, we'd be dropping the resolver parts of the feature (for now). See https://github.com/rust-lang/rust/issues/44663.

cargo fetch gets most of the way there. But you would need to build them as well to actually get good performance.

This is the upstream issue in question: https://github.com/rust-lang/cargo/issues/2644

Cargo fetch and/or cargo-chef kind of does these things, but not in a super intuitive and easy to use way.

opencv

There is an OpenCV bindings crate. This example might be what you're after https://github.com/twistedfall/opencv-rust/blob/master/examples/video_capture.rs

For example, this is the build script of the opencv bindings: https://github.com/twistedfall/opencv-rust/blob/master/build.rs

I’m trying to get around a known build issue—it would be great for it to be fixed upstream, but I don’t have any control over it except for setting OUT_DIR during its compilation.

I've been using https://github.com/twistedfall/opencv-rust a lot lately and it's really fantastic, they've done a great job matching up with how C++ works, so there are definitely good examples out there.

I never tried it, but the OpenCV bindings might work.

I thought it was going to be unsafe because of how Mat is implemented (more information here). ... I tested it and it should be fine memory-wise. My thought was that the code below was going to be allowed to compile.

I added opencv-rust as a dependency to a project. It makes my builds and even cargo check s really slow. It seems to invoke the build.rs script every time even when just type checking. Is this intentional? Is there any way to avoid this?