__traits(compiles,...) <=> ? is(typeof(...))

[Jonathan M Davis]

On Tuesday, October 30, 2012 00:29:22 Timon Gehr wrote:
> On 10/30/2012 12:17 AM, Jonathan M Davis wrote:
> > On Monday, October 29, 2012 23:38:34 Timon Gehr wrote:
> >> On 10/29/2012 12:03 PM, Jonathan M Davis wrote:
> >>> On Monday, October 29, 2012 11:42:59 Zhenya wrote:
> >>>> Hi!
> >>>> 
> >>>> Tell me please,in this code first and second static if,are these
> >>>> equivalent?
> >>>> with arg = 1, __traits(compiles,"check(arg);") = true,
> >>>> is(typeof(check(arg))) = false.
> >>> 
> >>> In principle, is(typeof(code)) checks whether the code in there is
> >>> syntatically and semantically valid but does _not_ check whether the
> >>> code
> >>> actually compiles. For instance, it checks for the existence of the
> >>> symbols
> >>> that you use in it, but it doesn't check whether you can actually use
> >>> the
> >>> symbol (e.g. it's private in another module).
> >>> ...
> >> 
> >> Accessing private symbols is always illegal, even within typeof
> >> expressions.> 
> > As I understand it, that's not supposed to be the case. is(typeof(T.init))
> > tests for existance not for compilability, and private symbols are fully
> > visible by everything that imports the module that they're in. They're
> > just
> > not accessible. I completely agree that it would be better for them to be
> > hidden as well, but it doesn't work that way right now, and no one has
> > been
> > able to convince Walter that it should.
> > ...
> 
> That is a different issue.

But as long as private symbols are visible, they should work with 
is(typeof(blah)), because it's testing for their existence, not whether they 
can be used or not..

- Jonathan M Davis