Re: std.algorithm.reduce on an array of structs

[Colin via Digitalmars-d-learn]

On Thursday, 11 September 2014 at 13:27:39 UTC, Daniel Kozak 
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.


You are try to put uint to Thing. This is corect version:

import std.stdio;
import std.algorithm;

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 ? a : b);  //  <-
Wont Compile
        writefln("%s", min2);
}

Ah ok. I get it.

Thanks daniel!