Difficulty in implementing a GCC plugin for [[invariant]] contract functions in classes/structs without prior experience?

[Gavin Ray <ray.gavin97@gmail.com>]

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Hey all,

The feature I appreciate most about the D programming language is its
"Design by Contract" feature.
Contract programming - Dlang Tour
<https://tour.dlang.org/tour/en/gems/contract-programming>

With the recent merge of Contracts to GCC master, C++ comes close to this,
with support for function-based contracts.
The most powerful contract though, is the "invariant" contract:

*invariant() is a special member function of struct and class types that
> allows sanity checking an object's state during its whole lifetime:*


>
> *- invariant() is called after the constructor has run and before the
> destructor is called.*
> *- invariant() is called before entering a member function*
> *- invariant() is called after exiting a member function.**- Class
> invariants are inherited. That means that a derived class invariant will
> implicitly call the base class invariant.*


I'm very interested in prototyping a GCC plugin to implement support for
transforming all member function calls in class/struct types
such that a call to the [[invariant]]-annotated function (if any) is placed
at the beginning and end of method bodies.

Does anyone have any idea whether something like this would be suitable for
a first plugin,
or if there would be roadblocks/technical challenges to implementing such a
thing?

I'd be grateful for any advice.

Thank you,
Gavin =)