use c++ 17 lambda function for progress_callback2

[farfromrefug]

Current Behavior

progress_callback2 is a function pointer

In my use case i need to use a c++ lambda function with capture as progress_callback2. Something like this:

int16_t lastProgress;
*monitor = tesseract::ETEXT_DESC();
monitor->progress_callback2 = [&] (tesseract::ETEXT_DESC* monitor, int left, int right, int top, int bottom) -> bool {
    int16_t progress = monitor->progress;
    if (progress > lastProgress) {
        lastProgress = progress;
    }
    progressLambda.value()(lastProgress);
    return true;
};

progressLambda is another lambda function which i pass a std::optional<std::function>

But this wont work because of the capture [&]. It is apparently not possible to cast it to function pointer

Expected Behavior

Being able to pass the lambda function

Suggested Fix

I managed to fix it replacing the type of PROGRESS_FUNC2 to:

using PROGRESS_FUNC2 = std::function<bool(ETEXT_DESC *, int, int, int, int)>;

I can make a PR for this but i want to be sure first that it would be something you would access.
I think it would be a breaking change because pointer function cannot be casted to std::function.

tesseract -v

No response

Operating System

No response

Other Operating System

No response

uname -a

No response

Compiler

No response

CPU

No response

Virtualization / Containers

No response

Other Information

No response

[zdenop]

The best way it create PR, it can be easily tested.

• some simple unittest

[danpla]

As a workaround, you can put your data in a local struct and access it via ETEXT_DESC::cancel_this.