On Sunday, 8 March 2015 at 20:36:34 UTC, anonymous wrote:
I get an error on your code: "test.d(16): Error: static assert
(canBeAlias!(true)) is false". But when commenting out the
first assert (line 15), there's no error.
Hmm, I might have made a mistake reducing my actual code.
Played around with it, and I think it's a bug in the compiler:
----
/* The differently numbered 'canBeAliasN' are all the same. */
enum true_ = true;
enum canBeAlias1(T...) = is(typeof({alias _ = T[0];}));
pragma(msg, canBeAlias1!true); /* "false" */
enum canBeAlias2(T...) = is(typeof({alias _ = T[0];}));
pragma(msg, canBeAlias2!true_); /* "true" */
enum canBeAlias3(T...) = is(typeof({alias _ = T[0];}));
pragma(msg, canBeAlias3!true, " ", canBeAlias3!true_); /*
"false false" */
enum canBeAlias4(T...) = is(typeof({alias _ = T[0];}));
pragma(msg, canBeAlias4!true_, " ", canBeAlias4!true); /* "true
true" */
----
On their own, `canBeAlias!true` = false and `canBeAlias!true_`
= true. This makes sense, because `true_` is a symbol whereas
`true` is a value.
But the two instantiations are apparently recognized as
equivalent. Whichever is instantiated first, its value is used
for the other instantiation, too. I think this behaviour is
wrong.
Yeah, definitely wrong.
template canBeAlias(T...)
if (T.length == 1)
{
static if (is(typeof({alias _ = T[0];})))
{
enum canBeAlias = true;
}
else
{
enum canBeAlias = false;
}
}
void main()
{
pragma(msg, canBeAlias!canBeAlias); //prints "true"
static assert(canBeAlias!(canBeAlias!canBeAlias)); //passes?!
static assert(!canBeAlias!true); //Error: static
assert(!true) is false
}
OR
void main()
{
pragma(msg, canBeAlias!canBeAlias); //prints "true"
static assert(!canBeAlias!true); //passes
//Error: static assert (canBeAlias!(true)) is false
static assert(canBeAlias!(canBeAlias!canBeAlias));
}
So it definitely does depend on which comes first. This is a
weird bug...
