On Friday, 2 September 2016 at 19:40:52 UTC, Meta wrote:
I was thinking about how to fix Typedef the other day and came
up with a way of generating a guaranteed unique ID for each
instantiation, even if they are on the same line:
[...]
What I'd like to know is if there might be a better way of
doing this. For each instantiation of FixedTypedef, there's a
new class being created and stored in the executable (I think),
as well as their .stringof. This could cause a lot of bloat if
Typedef is being used heavily.
IMHO, a better solution would be a __UNIQUE_UUID__ special token,
which the compiler replaces with a randomly generated (or
guaranteed unique, if we cannot afford a strong enough random
algorithm) UUID (or identifier, or whatever you prefer).
But if we cannot have it, a library function that does what you
propose may be useful, as unique strings may also be helpful in
other places.
Furthermore, would this be considered a code breakage? Looking
at http://dlang.org/phobos/std_typecons.html#.Typedef, it says:
"Typedef allows the creation of a unique type which is based on
an existing type. Unlike the alias feature, Typedef ensures the
two types are not considered as equals."
This implies that the current behaviour of Typedef is a bug,
and thus fixing it would not be code breakage. However, people
may have come to depend on this bug and fixing it would break
code. Thirdly, there is no point in having Typedef behave as it
currently does by default, which is similar to how aliases
behave. Example:
alias NewDouble = Typedef!double;
assert(!is(NewDouble == double)); //Okay, not the same type as
expected
alias NewInt1 = Typedef!int;
alias NewInt2 = Typedef!int;
assert(is(NewInt1 == NewInt2)); //Passes?!
I see the current behaviour not as a bug, but as a
not-well-documented feature. In fact, the current behaviour
allows you to create families of types which are considered
equal. This method is different from `alias`, as it is based on
strings and thus it does not require visibility of the aliased
type.
What we surely want is an easy way to guarantee that a Typedef is
in fact unique. This can be done with another template
`UniqueTypedef`, or having an easy way to generate unique strings
(see my idea above):
alias t = Typedef!(int, int.init, __UNIQUE_UUID__);
