These don't do short-circuit evaluation, and so I ran into some
some very subtle side-effects when converting code to DistinctNumeric.
In code like this:
MyDistinctNumeric n;
if (n && check_thing(n))
return;
There would be no short-circuit evaluation if the return type of
check_thing() was implicitly convertible to MyDistinctNumeric.
Ran into this while making Ext2FS::GroupIndex a DistinctNumeric.
Problem:
- `(void)` simply casts the expression to void. This is understood to
indicate that it is ignored, but this is really a compiler trick to
get the compiler to not generate a warning.
Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.
Note:
- Functions taking a `(void)` argument list have also been changed to
`()` because this is not needed and shows up in the same grep
command.
This template class allows for easy generation of incompatible numeric types.
This is useful whenever code has to handle heterogenous data (like meters and
seconds) but the underlying data types are compatible (like int and int).
The motivation comes from the Kernel's inconsistent use of pid_t for process and
thread IDs even though the ID spaces are incompatible, and translating forth/back
is nontrivial.
Other uses could be units (as described above), or incompatible index systems.
A popular use in real life is image manipulation, when there are multiple
coordinate systems.
