C#'s 'is' equivalent in D

[Jonathan M Davis]

On Thursday, October 10, 2019 9:47:58 AM MDT Just Dave via Digitalmars-d-
learn wrote:
> In C# you can do something like:
>
>
>      if (obj is Person)
>      {
>          var person = obj as Person;
>          // do stuff with person...
>      }
>
> where you can check the type of an object prior to casting. Does
> D have a similar mechanism? It's so widely useful in the C# realm
> that they even added syntactic sugar to allow:
>
>      if (obj is Person person)
>      {
>          // do stuff with person...
>      }
>
> I would presume since D has reference objects there must exist
> some mechanism for this...

D's solution is basically the same as C++'s solution. You cast and then
check whether the result is null. So,

if(cast(Person)obj !is null)
{
}

or since using a pointer or reference in an if condition checks whether it's
null or not

if(cast(Person)obj)
{
}

and you can even declare a variable that way if you want. e.g.

if(auto person = cast(Person)obj)
{
}

When D's is is used to compare two objects, it checks whether they're equal
bitwise. So, it's typically used for comparing pointers or references for
equality (whereas using == with references would compare the objects
themselves for equality).

- Jonathan M Davis