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!