On Tuesday, 10 July 2018 at 13:41:56 UTC, FeepingCreature wrote:
I've written up a short blogpost about the T.init issue.
It is not very enthusiastic.
https://medium.com/@feepingcreature/d-structs-dont-work-for-domain-data-c09332349f43
Related links:
https://github.com/dlang/phobos/pull/6594 problem with T.init
and toString
https://github.com/dlang/phobos/pull/6619 Nullable can't work
with types where T.init violates invariants
https://github.com/dlang/dmd/pull/8462 A somewhat sketchy PR to
disable invariant on struct ~this
First of all I must point that I would very much like to have
seen a code actually producing an error in that article. Contrary
to what is hinted just taking the struct and putting using it
with Nullable or format() caused no error for me and worked as
expected. Taking .init explicitely was the only thing that
actually caused an error. I'm not saying you didn't experience
these issues, but if you want to demonstrate a problem then
please demonstrate it.
That said, I may be missing something obvious but what prevents
you from overloading the init field?
struct MyDomainData {
string username;
@disable this(); // don't make a MyDomainData() by
accident!
this(string username)
in(!username.empty) // only non-empty usernames please!
do { this.username = username; }
// let's formalise the restriction.
invariant { assert(!username.empty); }
string toString() { ... }
static @property MyDomainData init() {
return MyDomainData("uninitialized");
}
...
}
auto test = MyDomainData.init; // There, no error
Of course that value means nothing but .init isn't meant to
actually mean something anyway, it's just a valid value and
that's what that init is proposing, so it shouldn't cause any
more bugs than empty .init in a normal case.
