On Sunday, 1 March 2015 at 15:49:12 UTC, Jakob Ovrum wrote:
On Sunday, 1 March 2015 at 15:40:06 UTC, Atila Neves wrote:
I've lost count now of how many times I've had to downgrade to
auto despite always wanting immutable or const. This doesn't
work:
auto reg = regex(`(foo)`);
const match = "foo".matchAll(reg);
writeln(match.captures); //oops, captures isn't const
It should, but it doesn't. Maxime talked about it here as well:
http://pointersgonewild.com/2014/07/11/the-constness-problem/
Atila
`match.captures` is a range; it's only natural for a range to
have mutable state to be iterable.
D's const is a bridge between immutable and mutable. const has
to be transitive because immutable is transitive. Don't use it
as if it was C++ const: there's no logical const in D, and if
there ever will be, it can't use the same `const` type
qualifier.
I know why it doesn't work. I know the reasons that go into the
design decision. const has to be the way it is or else
thread-safety goes out of the window. I'm not talking about
logical const; I'm talking about making as many things const and
immutable as I can to reduce the number of things I have to keep
in my mind at any given time.
const foo = getFoo(); //no need to reason about foo anymore, it
won't change
auto bar = getBar(); //oh-oh, now the next 50 lines can do
whatever they want with this
I shouldn't have to make captures const if all I want to do is
inspect the 3rd value. And yet I do. That was just one example,
like I said I've lost count of how many times I've changed const
to auto in my code because it wouldn't compile otherwise. I don't
go as far as Manu as use mutable everywhere, just where I have
to. And I'm always annoyed when it's the case.
Atila
