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Underscores

Underscores at the beginning of a name for certain things have a special meaning for the Py++ transpiler. They indicate that something is 'private'.

If you define a function (for example) in a Py++ source file starting with an underscore, then you should not import that function into some other file in your codebase. If you do, the C++ compiler will throw an error.

This is the case for the following:

  • functions
  • classes. I.e.:
    • normal classes
    • config classes
    • custom exceptions
    • interfaces
  • variables defined at the highest level of your Python module
  • type aliases defined at the highest level of your Python module

What is this useful for?

If you define something as private, then you don't have to worry about namespace conflicts with the rest of your codebase. Additionally, it could make C++ compilation slightly faster.

How does the Py++ transpiler do this?

When the Py++ transpiler sees one of these things starting with an underscore, it does not put the thing in the header file (only the .cpp file).