• DLearner (19/19) Aug 23 2021 Hi
• jfondren (37/56) Aug 23 2021 Perhaps you're thinking of note 12 in

DLearner <bmqazwsx123 gmail.com> writes:

Hi

The code below compiles and runs producing 'Not null'.

```
void main()
{
    import std.stdio;

    int Var1;
    int* ptrVar;

    ptrVar = &Var1;

    if (ptrVar == null) {
       writeln("Null");
    } else {
       writeln("Not null");	
    }
}
```

However, should it not fail to compile, as '==' used instead of 
'is'?

Best regards

jfondren <julian.fondren gmail.com> writes:

On Monday, 23 August 2021 at 13:00:36 UTC, DLearner wrote:
 Hi

 The code below compiles and runs producing 'Not null'.

 ```
 void main()
 {
    import std.stdio;

    int Var1;
    int* ptrVar;

    ptrVar = &Var1;

    if (ptrVar == null) {
       writeln("Null");
    } else {
       writeln("Not null");	
    }
 }
 ```

 However, should it not fail to compile, as '==' used instead of 
 'is'?

 Best regards

Perhaps you're thinking of note 12 in 
https://dlang.org/spec/expression.html#equality_expressions ?

Which ends:

"Comparing against null is invalid, as null has no contents. Use 
the is and !is operators instead."

But also begins:

"**For class objects**, the == and != operators are intended to 
compare the contents of the objects, however an appropriate 
opEquals override must be defined for this to work. The default 
opEquals provided by the root Object class is equivalent to the 
is operator."

ptrVal is just an int*, and == against it implies no attempt look 
for a opEquals.

Contrast:

```d
class S {
     int* p;
     this(int* p) {
         this.p = p;
     }
}

void main() {
     import std.stdio;

     int Var1;
     auto ptrVar = new S(&Var1);

     if (ptrVar == null) {
         writeln("Null");
     } else {
         writeln("Not null");
     }
}
```

Which fails to compile with

```
Error: use `is` instead of `==` when comparing with `null`
```