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templatestypestype-conversiondnullable

Maybe types in D

I'm trying to define a value type which either holds a size_t or a null (which is what I mean by a 'maybe type'). What I want to be able to do is something like this (where the relevant type is Maybe!size_t:

 Maybe!size_t something_which_could_fail (int foo) {
      if (foo < 0) { return null;}
      else { return foo;}
 }

How would I implement such a thing? Ideally, I would like to be able to make it a template (so I could have other Maybe types as well), and have conversions from maybe to non-maybe types be possible as above (although I don't mind typecasting if this is not possible). It would also be nice if I could do something like this:

Maybe!size_t a = 50;
Maybe!size_t b = null;
Solution

  • What about Nullable type in phobos library? http://dlang.org/phobos/std_typecons.html#.Nullable

    And some other info in D forum: D forum thread about Option(Maybe) type