Re: Open question: what code pattern you use usually for null safety problem

[ddcovery via Digitalmars-d-learn]

On Thursday, 14 January 2021 at 20:23:08 UTC, Steven 
Schveighoffer wrote:

You could kinda automate it like:
struct NullCheck(T)
{
   private T* _val;
   auto opDispatch(string mem)() if (__traits(hasMember, T, 
mem)) {
       alias Ret = typeof(() { return __traits(getMember, 
*_val, mem); }());
       if(_val is null) return NullCheck!(Ret)(null);
       else return NullCheck!(Ret)(__trats(getMember, *_val, 
mem));
   }

   bool opCast(V: bool)() { return _val !is null; }
}

auto nullCheck(T)(T *val) { return AutoNullCheck!T(val);}

// usage
if(nullCheck(person).father.father && person.father.father.name 
== "Peter")

Probably doesn't work for many circumstances, and I'm sure I 
messed something up.

-Steve

I'm seeing "opDispatch" everywhere last days :-). It's really 
powerful!!!

If we define an special T _(){ return _val; } method, then you 
can write

  if( nullCheck(person).father.father.name._ == "Peter")

And renaming

  if( ns(person).father.father.name._ == "Peter" )

And adding some extra check like ** isAssignable!(Ret, 
typeof(null) )** we can add special treatment for not nullable 
types

  if( ns(person).father.father.age._(0) == 92 ){ ... }
  assert( ns(person).father.father.father.age._ == int.init );

If for some strange reason I ever need null safety, I think this 
is the most beautiful solution or at least a great lesson on 
templates.

Thanks a lot for the lesson, Steve