By performing more pointer casting gymnastics, additional types of
pointer can be supported. For example, now const qualified pointers
can be passed through thanks to the use of constCast. Also, having
explicit ptrCast allows nested pointers (e.g. a pointer to a slice,
such as `*[]const u8`) to be passed as userdata as well (the compiler
refuses to coerce a pointer to a pointer to `?*anyopaque` for some
reason, I guess because maybe it's ambiguous somehow?) Hopefully this
extra casting does not appreciably reduce the compiler's ability to
catch real bugs (for example, on a 64-bit machine, ptrCast can convert
a *u64 into a **u64 because there is no alignment change).
Also, the `volatile` pointer specifier is still not supported.
`allowzero` pointers probably also have a problem. Those are both
extreme edge cases, however.
This was intended to work before but did not due to an oversight.
Specifically, because the userdata pointers are stored as ?*anyopaque,
which does *not* have the const qualifier, they must have their const
qualifiers also removed. This is safe because the thunk guarantees
that the consumer code never sees the non-const version of the
pointer, and the nats library itself does nothing except pass the
pointer through to the user callback.
The tests have been updated to ensure this case works. The examples
still use a mutable userdata pointer to show that that case also
works. More tests could be added for the sake of increased rigor, but
I don't think it adds much.
torque
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