On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:
On Tuesday, 4 July 2017 at 23:26:28 UTC, H. S. Teoh wrote:
On Tue, Jul 04, 2017 at 11:27:25PM +0000, Jean-Louis Leroy via
Digitalmars-d-learn wrote:
I want to create a range that consists of the result of a map()
followed by a value, e.g.:
int[] x = [ 1, 2, 3];
auto y = map!(x => x * x)(x);
auto z = y ~ 99; // how???
I have tried several variations: convert 99 to a dynamic array, to a
range, convert range to dynamic array (couldn't even figure that
one); to no avail.
[...]
Try:
auto z = chain(y, only(99));
Thanks!
However, when I try to use this construct in my real code, I still have
a problem:
// k is a ClassInfo
chain(map!(i => i.classinfo)(k.interfaces), only(k.base))
meth.d(311): Error: template std.range.chain cannot deduce function from
argument types !()(MapResult!(__lambda3, Interface[]),
OnlyResult!(TypeInfo_Class, 1LU)), candidates are:
/usr/include/d/std/range/package.d(795):
std.range.chain(Ranges...)(Ranges rs) if (Ranges.length > 0 &&
allSatisfy!(isInputRange, staticMap!(Unqual, Ranges)) &&
!is(CommonType!(staticMap!(ElementType, staticMap!(Unqual, Ranges))) ==
void))
No time to dig deeper but this is because the two ranges that chain()
receives do not have a common type. (Rather, that type is 'void'):
import std.algorithm;
import std.range;
import std.traits;
class C {
}
void main() {
auto k = C.classinfo;
auto m = map!(i => i.classinfo)(k.interfaces);
auto b = only(k.base);
// Types
alias M = typeof(m);
alias B = typeof(b);
// Element types
alias EM = ElementType!M;
alias EB = ElementType!B;
// Two of chain's constraints are satisfied:
static assert(isInputRange!M);
static assert(isInputRange!B);
// Now it needs to see a CommonType of range elements
pragma(msg, EM); // const(void)[]()
pragma(msg, EB); // const(void)[]()
pragma(msg, CommonType!(EM, EB)); // void
// For that reason, the following does not work:
// chain(m, b);
}
Ali
