Adding a way to set the value of `cling::utils::out`

[MostafaNanticock]

We have a project that uses Cling to add the ability to do some actions using c++ at runtime.
currently the only way for us to show the user the result of executing a line such as int a = 5 is through std::cout.
The problem is, we are already using std::cout to print out many things like when logging is enabled in the application.

Take this output for example:

[INFO] started interactive c++ console
[cling]$ int a = 5
(int) 0
[cling]$ auto pvw = createNewPlotViewWindow()
[INFO] Creeating a new PlotViewWindow...
[INFO] Initializing OpenGL...
[INFO] Using OpenGL version 4.6
[INFO] OpenGL vendor: NVIDIA Corporation
[INFO] OpenGL renderer: Quadro T2000/PCIe/SSE2
[INFO] is OpenGLES: false
[INFO] OpenGL version: 4.6
[INFO] OpenGL options: 
    depthBufferSize 24,
    redBufferSize 8,
    greenBufferSize 8,
    blueBufferSize 8,
    alphaBufferSize 8,
    stencilBufferSize 8,
    samples 0,
    swapBehavior DoubleBuffer,
    swapInterval 1,
    colorSpace sRGBColorSpace
[INFO] OpenGL initialization finished
[INFO] Window initialization done
(PlotViewWindow *) 0x7dff598e91
[cling]$

and as you can see it becomes so frustrating especially when the user tries to scroll back through the terminal to check his previous inputs.
And after thorough examination of the Cling source code, it appears that the best solution would be for us to implement our own llvm::raw_os_ostream that we can then use as the default cling::utils::outs, cling::utils::errs and cling::utils::logs,
This would also allow us to integrate the logging library that we are using with Cling directly, so that it can simply log any cling message or error at real-time.

I don't know if there is any reason behind the choice for not having this functionality, and it's fairly easy to implement.
The simple solution that i can think of right now would be to add three functions in the form of:

namespace cling::utils {
    void setOuts(llvm::raw_ostream &newOuts);
    void setErrs(llvm::raw_ostream &newErrs);
    void setLog(llvm::raw_ostream &newLog);
}

I'd be happy to submit a pull request with this simple addition if any of the maintainers agreed on this proposed change.

[ferdymercury]

Did you try with any of the redirection commands?

   .> <filename>		- Redirect command to a given file
      '>' or '1>'		- Redirects the stdout stream only
      '2>'			- Redirects the stderr stream only
      '&>' (or '2>&1')		- Redirects both stdout and stderr
      '>>'			- Appends to the given file

I'd be happy to submit a pull request with this simple addition if any of the maintainers agreed on this proposed change.

adding @hahnjo or @vgvassilev to the loop.

[MostafaNanticock]

Yes, I know about the ability to redirect output to files, But the way it's implemented is by redirecting the c++ std::cout and std::cerr streams to a given file. Which doesn't solve the original problem.

Consider running the following example after redirecting stdout to a given file:

[cling]$ std::cout << "Hello" << std::endl;

This will cause the word 'Hello' to be outputted to the file, which isn't what we want.

What we want is to have some way to only redirect the outputs of cling itself. Whether it's a warning, an error or just the immediate output of executing any statement without adding the semicolon to the end.
For example, when you execute this line:

[cling]$ std::cout << "Hello" << std::endl

the output would be:

Hello
(basic_ostream<char, std::char_traits<char> > &) @0x7ff98e524fc0

where the first line is just the result of appending stuff to std::cout and the second output is the result of executing the line inside cling

We want to be able to only redirect Cling output

[ferdymercury]

Thanks for the clarification. If you consider proposing a PR, it should be done directly here: https://github.com/root-project/root/pulls under interpreter/cling subdirectory.

[MostafaNanticock]

Should i raise an issue there first in order to make sure that this modification doesn't conflict with anything, or it's ok to go there and make the pull request directly?

[ferdymercury]

The issue can stay here, no need to transfer.
You can already put the Pull Request directly there, and you can write Fixes https://github.com/root-project/cling/issues/530 as second line of the commit.