ddash.functional.pred

1 static struct S(alias pred) {
2     auto f(int a, int b) {
3         static if (isEq!pred) {
4             return pred(a, b);
5         } else static if (isLt!pred) {
6             return !pred(a, b) && !pred(b, a);
7         } else {
8             import std.functional: binaryFun;
9             return binaryFun!pred(a, b);
10         }
11     }
12 }
13 
14 alias A = S!(eq!((a, b) => a == b));
15 alias B = S!(lt!((a, b) => a < b));
16 
17 assert( A().f(1, 1));
18 assert( B().f(1, 1));
19 assert(!A().f(2, 1));
20 assert(!B().f(2, 1));
21 
22 static bool feq(int a, int b) { return a == b; }
23 static bool flt(int a, int b) { return a < b; }
24 
25 alias C = S!(eq!feq);
26 alias D = S!(lt!flt);
27 
28 assert( C().f(1, 1));
29 assert( D().f(1, 1));
30 assert(!C().f(1, 2));
31 assert(!D().f(1, 2));
32 
33 assert(S!"a == b"().f(1, 1));