I'm trying to figure out how to test whether a UDA struct was
initialized with arguments (and change the behavior of the
surrounding code if it was. While I was tinkering around with
test files, I came up with this little gem:
import std.traits;
struct Attr
{
string str;
}
@Attr("test")
void foo(){}
@Attr
void bar(){}
void main()
{
alias UDA = getUDAs!(bar, Attr)[0];
static if (__traits(hasMember, UDA, "str"))
{
static if (__traits(compiles, __traits(getMember, UDA,
"str")))
{
__traits(getMember, UDA, "str"); // Compile error!
need 'this' for 'str' of type 'string'
}
}
}
I can rationalize what the error means -- the compiler wasn't
given a string so it requires a concrete object to get the member
from. What I don't understand is why *both* of those static ifs
passed. If it has the member and I can't get it, and if getting
the member compiles yet at the same time it doesn't, I'm not sure
how I can actually make this test work.
It would make sense if the attribute over bar wasn't semantically
valid, but I can use it in every other way *except* getting the
string field out of it.
Am I missing something obvious here?
