Is there a simple way to check if value is null for every case?

[vit]

On Monday, 27 August 2018 at 12:54:59 UTC, SG wrote:
> On Monday, 27 August 2018 at 03:21:04 UTC, rikki cattermole 
> wrote:
>> Templates make it the easiest way, since common patterns, like 
>> arrays, classes and pointers have the exact same null check 
>> syntax.
>
> I see.
>
>> That code is only for classes. C# also has structs which are a 
>> value type. Which it would not work for.
>
> The same thing for struct in C#
>
> Struct S{
>    public int? i;
> }
>
> S.i == null; // This works nicely.
>
>> You don't need isNull function for Nullable because it has a 
>> method called it. That will be preferred (hence I specifically 
>> used isNull as the name).
>>
>> For Variant, use hasValue.
>>
>> bool isNull(Variant value) {
>> 	return !value.hasValue;
>> }
>
> The problem I'm trying to solve is beyond that. This is just an 
> example. But bear with me, right now all I want is a function 
> to check the value from 'a' type and return if it is null.
>
> The type could be a: Class, Struct, a Basic data type, Variant, 
> Nullable and so.
>
> And what I see, these types has different behaviors, while in 
> C# at least for this same case, I would write the same thing in 
> few lines to perform it, in D I found very hard.
>
> Isn't counter intuitive the way D works? Because for each type 
> Class/Nullable you check with .isNull, for Variant with 
> .hasValue, for string (variable is null).
>
> Thanks.

hasValue isn't equivalent of isNull or is null. 'null' is valid 
value in Variant:


         import std.variant;
         Variant v;

         v = null;
         assert(v.hasValue);		       //v has value
         assert(v.get!(typeof(null)) is null);  //value in v is 
null

Nullable!T.isNull isn't equivalent of is null:

     	int* i = null;
     	Nullable!(int*) ni;
     	ni = i;
         assert(ni.isNull == false);	///ni has value
         assert(ni is null);	        ///ni value is null

string is null isn't equivalent of empty:

     	string str = "test";
     	str = str[0 .. 0];
         assert(str !is null);	///str isn't null
         assert(str.empty);	///str is empty