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