Flag proposal

[David Nadlinger]

On 6/11/11 1:54 PM, Andrei Alexandrescu wrote:
> Consider two statements:
>
> 1. "I dislike Flag. It looks ugly to me."
>
> 2. "I dislike Flag. Instead I want named arguments."
>
> There is little retort to (1) - it simply counts as a vote against. For
> (2) the course of action is to point out the liabilities of changing the
> language.

*And*, at least for me, still count it as an (informal) vote against 
Flag. You wrote about »The point is it [named arguments] would also have 
disadvantages«, but at the same time, you seem to ignore that using a 
non-obvious construct all over the standard library adds to perceived 
the »language complexity« (from the user's perspective) just as well, 
even more so if opDispatch or other »hacks« are used to beautify the 
implementation.

Yes, I do think named parameters would be a step forward and we should 
definitely look into adding them to D. But independently, I don't think 
that reinventing bool in Phobos is a good idea. How would you explain 
somebody new to D that, while usually it's »Something.property«, you 
have to write »Yes.foo« instead of »Foo.yes«? Also, there is the issue 
of error messages:

---
void foo(Flag!"bar" flag) {}

void main() {
   foo(No.baz);
}
---

leads to

---
Error: function foo (Flag flag) is not callable using argument types (Flag)
Error: cannot implicitly convert expression (opDispatch()) of type Flag 
to Flag
---

I don't know about you, but I think this is not quite an acceptable 
error message for mistyping a single character while trying to pass a 
boolean parameter to some standard library function.

David