On Sunday, 31 January 2016 at 21:22:06 UTC, SimonN wrote:
Hi,
we start with the following code snippet, which works.
import std.algorithm;
import std.range;
import std.stdio;
class A { int val; }
class B : A { this() { val = 3; } }
class C : A { this() { val = 4; } }
B[] b = [new B(), new B()];
C[] c = [new C(), new C()];
void main()
{
chain(b, c).each!(a => a.val.writeln);
}
The output, as expected, is:
3
3
4
4
Now I change the declarations of B[] b and C[] c to the
following, keeping
everything else in the code snippet the same:
const(B[]) b = [new B(), new B()];
const(C[]) c = [new C(), new C()];
This makes dmd 2.070 choke: (
http://dpaste.dzfl.pl/eee69fd03dd9 )
Error: template std.range.chain cannot deduce function from
argument
types !()(const(B[]), const(C[])),
candidates are:
/opt/compilers/dmd2/include/std/range/package.d(804):
std.range.chain(Ranges...)(Ranges rs) if (Ranges.length > 0
&&
allSatisfy!(iseputRange, staticMap!(Unqual, Ranges)) &&
!is(CommonType!(
staticMap!(ElementType, staticMap!(Unqual, Ranges))) ==
void))
What's stumping me -- constness doesn't make dmd choke on
ranges of
numbers. If I replace the classes B and C with simple 'int' and
'double',
this compiles again:
const(int[]) b = [1, 2];
const(double[]) c = [3.3, 4.4];
void main() { chain(b, c).each!(a => a.writeln); }
Why does it fail for const(array of class)?
Is any template magic about Unqual or staticMap relevant here?
-- Simon
types !()(const(B[]), const(C[])),
candidates are:
/opt/compilers/dmd2/include/std/range/package.d(804):
std.range.chain(Ranges...)(Ranges rs) if (Ranges.length > 0
&&
allSatisfy!(iseputRange, staticMap!(Unqual, Ranges)) &&
!is(CommonType!(
staticMap!(ElementType, staticMap!(Unqual, Ranges))) ==
void))
Unqaul means remove any const or immutable torn the type
StaticMap is like a compile time map
What this error message says is that there is one candidate
function that matches what you are attempting to do. and that
chain takes a variadic argument and each of those arguments must
1) when unqualified be an input range (Basically you can foreach
over it)
2) that the common type of the element type of the unqualified
variadic argument types is not void (in this case not arrays of
void)
Have you tried changing The declaration of a and b to const(A[])?
Also have you tried with other reference type (e.g. assoc arrays
pointers)?
Nic
