`{:ok, ...}` is too verbose`!`

[cocoa-xu]

`{:ok, ...}` is too verbose`!`

[josevalim]

{:error, "empty matrix"} love it! Or {:error, "null matrix"}. :)

[cocoa-xu]

Massive thanks to @josevalim for the Errorize demo code. Works like a charm!

[cocoa-xu]

Notes, for some functions, OpenCV decides to print warnings (tested on OpenCV 4.5.5) instead of reporting error to us, i.e., the NIFs.

For example, for the imread function

iex(1)> mat = OpenCV.imread!("/path/to/non/exist/image.png")
[ WARN:0@0.008] global /Users/cocoa/Git/evision/3rd_party/opencv/opencv-4.5.5/modules/imgcodecs/src/loadsave.cpp (239) findDecoder imread_('/path/to/non/exist/image.png'): can't open/read file: check file path/integrity
iex(2)> mat
nil

[josevalim]

@cocoa-xu can you configure it to return an error instead? 🤔

[cocoa-xu]

This seems to be its intended behaviour, according to their docs

The function imread loads an image from the specified file and returns it. If the image cannot be
read (because of missing file, improper permissions, unsupported or invalid format), the function
returns an empty matrix ( Mat::data==NULL )

And since everything is immutable in Erlang/Elixir, I think returning a nil instead of returning a reference to an empty mat is probably fine?

[josevalim]

I see, makes sense. It would be nice if we could return {:error, "no result"} in this case but I understand it may be hard to automate this.

[cocoa-xu]

In C++, OpenCV returns a valid cv::Mat object but everything is 0.

cv::Mat img = cv::imread("/dev/null");
std::cout << img.cols << "\n";
// output: 0

In opencv-python, the result is None

>>> import cv2
>>> mat = cv2.imread("/dev/null")
>>> mat is None
True

But sure, I can return an error tuple for this. However, I can only do this for general like when converting from cv::Mat to ERL_NIF_TERM.

Perhaps we could return {:error, "empty matrix"}?