Enhancing CMakePPLang with Frozen Maps / Objects

[Xyphenore]

Great job on this project! I've been searching for something like this to enhance my CMake scripts and incorporate a map container. It's unfortunate that your work hasn't gained enough popularity yet.

Problem description
In Python, there is often a need to create immutable maps and lists that prevent the addition or removal of values. I use maps to store constants such as file hashes, which should remain unchanged during execution. However, currently, I am able to modify the map containing file hashes. I would like the map to be constant, similar to how it behaves in C++.

Requested solution
I suggest adding a member function to freeze an object, specifically a map. When an object is frozen, the 'set' function should throw an exception and prevent any modifications to the object.

Considered alternatives
One alternative I've considered is using a keyword in the constructor to directly create a frozen map without the need for a separate 'freeze' function.

Note: Please ensure that the implementation also accounts for thawing or unfreezing an object if needed.

[ryanmrichard]

@Xyphenore Just to make sure I understand you correctly, do you want map objects to behave like (I'm using int as a placeholder for any non-cv-qualified type):

• const std::map<int, int> (entire map is read-only),
• std::map<int, int> (only the keys are read-only, but can be added/deleted),
• std::map<int, const int> (keys and values are read-only, but can be added/deleted),
• or something else?

In theory the second option should be how the map objects already behave (although I will admit I'm not sure we have explicitly tested that this is the case; if it is not I would consider that a bug that needs fixed).

Regardless, I think this is a great suggestion. Const-ness/immutability is something that is missing from CMakePPLang in general. We've been modeling CMakePPLang after Python so I'd be inclined to, as a first step, introduce a Tuple class which is immutable once created. With a Tuple object we could make a FrozenMap class pretty easily.

[Xyphenore]

The first thing 'const std::map<int, int>' is what I need. This map contains keys and values, but it does not allow adding or removing values, similar to the FrozenMap object in Python.