On Thursday, 28 March 2013 at 18:24:19 UTC, Timon Gehr wrote:
(...)
Indeed, the above code should not compile. My upcoming D front
end currently reports the following after fixing the
grammatical mistakes (For now. The error message text should
maybe be improved. Ideas welcome.)
tt.d:2:32: error: declaration of 'x' smells suspiciously fishy
static if (!is(typeof(y))) int x = 1;
^
tt.d:1:23: note: this lookup should have succeeded if it was
valid
static if (!is(typeof(x))) int y = 1;
^
tt.d:1:32: error: declaration of 'y' smells suspiciously fishy
static if (!is(typeof(x))) int y = 1;
^
tt.d:2:23: note: this lookup should have succeeded if it was
valid
static if (!is(typeof(y))) int x = 1;
^
Surely it will be fun to work with (though 'this lookup' message
is somewhat confusing)!
There are lots of similar analysis order issues without static
if. (Luckily, they can be detected well enough conservatively
in a quite general way.) The following is a simplified example
from my test suite:
class A{ int string; }
template Mixin(string s){
mixin("alias "~s~" Mixin;");
}
class D: Mixin!({D d = new D; return d.foo();}()){
int foo(int x){ return 2;}
string foo(){ return "A"; }
}
The problem is of course that 'string' has to be resolved in
order to compute the parent of 'D'. However, that parent then
changes the meaning of 'string' in the subclass scope.
Therefore, the code is meaningless.
I am lost here. Are 'int string' in A in and 'int foo(int)' in D
relevant? Shouldn't this example fail simply because in order to
process the declaration of D the compiler needs to instantiate D
in the delegate body? So this would be similar to:
template Mixin(bool b : true) {
alias Object Mixin;
}
class D: Mixin!(new D == new D) {}
Artur
