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

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

void main()
{
   import std.stdio;

   int Var1;
   int* ptrVar;

   ptrVar = &Var1;

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

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:

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`