DMD can implicitly convert class pointer to the bool. Is it bug or terrible feature?

[bearophile]

Andrei Alexandrescu:

> I'm not sure whether shadowing globals or members would be a 
> good idea.

I understand. It's not a clear cut topic. There are real reasons 
both for and against this idea. But surely it should be 
considered. I have not yet (re)opened an enhancement request on 
this.


> gcc has a -W flag for that, and someone tried to turn it on at 
> Facebook but with debatable results. We ended up not using that 
> warning.

In the example I have shown it's with() that is uncovering a 
struct field with the same name of a module-level name. So it's 
not exactly the same as a local variable shadowing a module-level 
name (and currently with has anti-hijacking for local variables). 
I think that shadowing module-level names with with() is not 
good. Also because of this idea:
https://d.puremagic.com/issues/show_bug.cgi?id=6917

Regarding Facebook, I presume that Gcc flag was applied to plenty 
of already written code. If you apply it since the start of a new 
project perhaps (probably) its effects are different. This detail 
is important, because lot of D code is yet to be written.

Regarding more generally the topic of shadowing module-level 
names with local names, the attribute "pure" helps avoid some 
cases, because you can only shadow immutable global names, and 
this is a little less dangerous/troublesome.

Time ago I suggested an optional @outer() attribute, that's 
useful to specify what names from outer scopes a function/method 
is allowed to see and use. It looks a bit excessive, but it shows 
that I have hated bugs caused by shadowing globals silently.

An IDE could underline the shadowing variables, turning the 
silent shadowing into a visible one, without giving warnings 
(it's a kind of much noisy warning), but unfortunately a compiler 
like dmd can't do that.

Another problem is that a command like "import std.algorithm" 
imports lot of names in the current module, and this could cause 
many false alarms. But this could be a good thing, and it can 
push Phobos devs to add more "private" tags to Phobos names, and 
D developers to add more qualified imports in their programs.

Bye,
bearophile