I've got a template that takes in a type. Sometimes the type is a class, sometimes a struct, sometimes just an int. It doesn't much matter what it is, but if it's a reference type I need to check if it's null so I can make it not null before using it. I get an error if I try to check if a value type is null so I'd like to put a "static if" to check if the type passed to the template is a nullable one so I can avoid checking the value types passed in. What do I have to do to check for nullability?

On Sunday, 7 June 2015 at 15:17:27 UTC, 1967 wrote:
> I've got a template that takes in a type. Sometimes the type is a class, sometimes a struct, sometimes just an int. It doesn't much matter what it is, but if it's a reference type I need to check if it's null so I can make it not null before using it. I get an error if I try to check if a value type is null so I'd like to put a "static if" to check if the type passed to the template is a nullable one so I can avoid checking the value types passed in. What do I have to do to check for nullability?

You can directly check whether it allows comparison with null:

    static if(is(typeof(value is null) : bool)) {
        if(value is null)
          ...
    }

On Sunday, 7 June 2015 at 15:39:17 UTC, Marc Schütz wrote:
> On Sunday, 7 June 2015 at 15:17:27 UTC, 1967 wrote:
>> I've got a template that takes in a type. Sometimes the type is a class, sometimes a struct, sometimes just an int. It doesn't much matter what it is, but if it's a reference type I need to check if it's null so I can make it not null before using it. I get an error if I try to check if a value type is null so I'd like to put a "static if" to check if the type passed to the template is a nullable one so I can avoid checking the value types passed in. What do I have to do to check for nullability?
>
> You can directly check whether it allows comparison with null:
>
>     static if(is(typeof(value is null) : bool)) {
>         if(value is null)
>           ...
>     }

Don't forget [`Nullable`][0] type, which won't pass this check.

[0]: http://dlang.org/phobos/std_typecons.html#.Nullable

On Sunday, 7 June 2015 at 15:17:27 UTC, 1967 wrote:
> I've got a template that takes in a type. Sometimes the type is a class, sometimes a struct, sometimes just an int. It doesn't much matter what it is, but if it's a reference type I need to check if it's null so I can make it not null before using it. I get an error if I try to check if a value type is null so I'd like to put a "static if" to check if the type passed to the template is a nullable one so I can avoid checking the value types passed in. What do I have to do to check for nullability?

A simple test:

http://dpaste.dzfl.pl/3b8c5a0bb69c