[Issue 8304] New: writeln of empty Nullables too
d-bugmail at puremagic.com
d-bugmail at puremagic.com
Tue Jun 26 16:28:03 PDT 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8304
Summary: writeln of empty Nullables too
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Keywords: rejects-valid
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody at puremagic.com
ReportedBy: bearophile_hugs at eml.cc
--- Comment #0 from bearophile_hugs at eml.cc 2012-06-26 16:30:32 PDT ---
In D you can't print an empty Nullable:
import std.stdio: writeln;
import std.typecons: Nullable;
void main() {
Nullable!int ni;
writeln(ni);
}
DMD 2.060alpha:
object.Exception at C:\dmd2\src\phobos\std\typecons.d(1218): Enforcement failed
But I'd like something similar to Haskell, where you are allowed to print an
empty Nullable (named Maybe):
...>ghci
GHCi, version 7.0.2: ...
Prelude> import Data.Maybe
Prelude Data.Maybe> Nothing :: Maybe Int
Nothing
In D when the Nullable is empty I'd like writeln to print something like
"EmptyNullable".
As temporarily workaround I've added this method to Nullable, but it's not a
good general solution:
string toString() const
{
return this.isNull ? "EmptyNullable": text(get());
}
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