Should StackTrace::operator[](size_t idx) be declared const?

[travisdowns]

Semantically it seems like StackTrace::operator[](size_t idx) is a const operation, since it is simply returning by value a Trace object constructed out of the current state of the stack traces, but it is not currently declared const.

This impedes some uses, the obvious ones being that you have to pass around a non-const StackTrace object to methods that might use [], but I ran into the case where a StackTrace member of another class couldn't be accessed with operator[] in a const function of the containing class.

The current (Linux) implementation of operator[] doesn't have any problem being declared const. Adding const should be a non-breaking change, although you couldn't rule out that some other implementation would want to make this a physically non-const operation (e.g., caching values, whatever) - but that's where mutable comes in.

[bombela]

Seems reasonable, thank you for the detailed proposal. Feel free to propose a pull request :)

[travisdowns]

Thanks, I submitted a PR.