On Thursday, 11 September 2014 at 13:28:37 UTC, Marc Schütz wrote:
On Thursday, 11 September 2014 at 13:06:05 UTC, Colin wrote:
I have this test code:
struct Thing {
uint x;
}
void main(){
uint[] ar1 = [1, 2, 3, 4, 5];
auto min1 = ar1.reduce!((a,b) => a < b);
writefln("%s", min1); // prints 1 as expected
Thing[] ar2 = [Thing(1), Thing(2), Thing(4)];
auto min2 = ar2.reduce!((a,b) => a.x < b.x); // <- Wont
Compile
writefln("%s", min2);
}
The line with "Wont Compile" on it has this error message:
/usr/include/dmd/phobos/std/algorithm.d(770): Error: cannot
implicitly convert expression (__lambda2(result,
front(_param_1))) of type bool to Thing
/usr/include/dmd/phobos/std/algorithm.d(791): Error: template
instance t.main.reduce!((a, b) => a.x < b.x).reduce!(Thing,
Thing[]) error instantiating
t.d(16): instantiated from here: reduce!(Thing[])
Any idea what I'm doing wrong here?
To me, the operation on ar2 should be pretty much identical to
ar1, except for the use of the struct.
I think you want to use `filter()` (for both Thing and uint),
not `reduce()`.
Scratch that, `filter()` doesn't make sense here, of course. The
rest is still valid:
The former produces a range with only the elements that match
the predicate, while the latter produces _one_ element
according to the given rules, e.g.
my_int_array.reduce!((result,a) => result+a);
produces the sum of all elements. In your example, the first
use only compiles because `bool` happens to be implicitly
convertible to `uint`.
