The D Programming Language's Unofficial Docs
beta
The D Programming Language's Unofficial Docs
beta
The wrapped type for which Nullable provides a null value.
The null value which denotes the null state of this Nullable. Must be of type T.
1 Nullable!(size_t, size_t.max) indexOf(string[] haystack, string needle) 2 { 3 //Find the needle, returning -1 if not found 4 5 return Nullable!(size_t, size_t.max).init; 6 } 7 8 void sendLunchInvite(string name) 9 { 10 } 11 12 //It's safer than C... 13 auto coworkers = ["Jane", "Jim", "Marry", "Fred"]; 14 auto pos = indexOf(coworkers, "Bob"); 15 if (!pos.isNull) 16 { 17 //Send Bob an invitation to lunch 18 sendLunchInvite(coworkers[pos]); 19 } 20 else 21 { 22 //Bob not found; report the error 23 } 24 25 //And there's no overhead 26 static assert(Nullable!(size_t, size_t.max).sizeof == size_t.sizeof);
import std.exception : assertThrown; Nullable!(int, int.min) a; assert(a.isNull); assertThrown!Throwable(a.get); a = 5; assert(!a.isNull); assert(a == 5); static assert(a.sizeof == int.sizeof);
auto a = nullable!(int.min)(8); assert(a == 8); a.nullify(); assert(a.isNull);
Just like Nullable!T, except that the null state is defined as a particular value. For example, Nullable!(uint, uint.max) is an uint that sets aside the value uint.max to denote a null state. Nullable!(T, nullValue) is more storage-efficient than Nullable!T because it does not need to store an extra bool.