[Octave-bug-tracker] [bug #59192] unwind_protect objects should accept lambda expressions

[John W. Eaton]

Follow-up Comment #2, bug #59192 (project octave):

Copying my comments from the discourse thread:

I recommend that you use an unwind_action object instead of unwind_protect.
The unwind_action object can only perform one cleanup action, but it can
already handle std::function objects and lambda expressions. Using that object
is also more efficient than unwind_protect because the unwind_protect object
must instantiate a std::stack object to hold the list of actions.

Separately, we might want to deprecate the unwind_protect object? It
originally made sense because there was a single global stack of actions and a
set of functions to operate on that stack. But then Jaroslav converted it to
use the present structure in which the actions are managed on a per-scope
basis using the destructor of the unwind_protect object. But we only ever need
to protect a few things (at most) in a given scope, so the overhead of
creating the std::stack object can be significant. In nearly all cases, it
probably makes more sense to just use a set of unwind_action variables instead
of a single unwind_protect object.

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