1 import std.traits : isUnsigned;
2
3 static struct MyHook
4 {
5 static bool thereWereErrors;
6 static int hookOpCmp(L, R)(L lhs, R rhs)
7 {
8 static if (isUnsigned!L && !isUnsigned!R)
9 {
10 if (rhs < 0 && rhs >= lhs)
11 thereWereErrors = true;
12 }
13 else static if (isUnsigned!R && !isUnsigned!L)
14 {
15 if (lhs < 0 && lhs >= rhs)
16 thereWereErrors = true;
17 }
18 // Preserve built-in behavior.
19 return lhs < rhs ? -1 : lhs > rhs;
20 }
21 }
22 auto a = checked!MyHook(-42);
23 assert(a > uint(42));
24 assert(MyHook.thereWereErrors);
25 static struct MyHook2
26 {
27 static int hookOpCmp(L, R)(L lhs, R rhs)
28 {
29 // Default behavior
30 return lhs < rhs ? -1 : lhs > rhs;
31 }
32 }
33 MyHook.thereWereErrors = false;
34 assert(Checked!(uint, MyHook2)(uint(-42)) <= a);
35 //assert(Checked!(uint, MyHook2)(uint(-42)) >= a);
36 // Hook on left hand side takes precedence, so no errors
37 assert(!MyHook.thereWereErrors);
38 assert(a <= Checked!(uint, MyHook2)(uint(-42)));
39 assert(MyHook.thereWereErrors);
The D Programming Language's Unofficial Docs
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Compares this against rhs for ordering. If Hook defines hookOpCmp, the function forwards to hook.hookOpCmp(get, rhs). Otherwise, the result of the built-in comparison operation is returned.
If U is also an instance of Checked, both hooks (left- and right-hand side) are introspected for the method hookOpCmp. If both define it, priority is given to the left-hand side.