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digitalmars.D.learn - Anything in D to avoid check for null everywhere?

reply Jack <jckj33 gmail.com> writes:
I was looking for a way to avoid null checks everywhere. I was 
checking the Null object pattern, or use something like enforce 
pattern, or even if I could make a new operator and implement 


Kotlin also got something in this area[2]

What some D ways to avoid those checks?

[1]: 
https://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000047.html
[2]: 
https://kotlinlang.org/docs/reference/null-safety.html#safe-calls
Jan 12 2021
next sibling parent Jack <jckj33 gmail.com> writes:
Currently I'm with this:

auto ref ifNotNull(T, T2)(T lhs, lazy T2 rhs)
{
     if(lhs) {
         rhs();
     }
     return lhs;
}


far from good. I wish there was a way to create a new operator so 


evaluate to null, probably due to lack of control of flow 
structure, which isn't possible within a source code, only from 
compiler's side, as far i know)
Jan 12 2021
prev sibling next sibling parent reply ddcovery <antoniocabreraperez gmail.com> writes:
On Tuesday, 12 January 2021 at 21:37:11 UTC, Jack wrote:

 I was looking for a way to avoid null checks everywhere. I was 
 checking the Null object pattern, or use something like enforce 
 pattern, or even if I could make a new operator and implement 


 actually), Kotlin also got something in this area[2]

 What some D ways to avoid those checks?

 [1]: 
 https://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000047.html
 [2]: 
 https://kotlinlang.org/docs/reference/null-safety.html#safe-calls


Personally, I really like functional orientation (MayBe, None, 
Some... and pattern matching) avoiding the use of null, but D is 
a "system" language compatible with C and null is mandatory.

Some months ago I wrote an utility template to simulate the ?. 
mechanism.


The resulting syntax:

   class Person
   {
     string name;
     Person father;

     this(string name, Person father){	
       this.name=name;
       this.father=father;
     }
   }

  Person p = new Person("Peter", new Person("John", null));
  assert( p.d!"father".d!"father".d!"name".get is null);
  assert( p.d!"father".d!"name".get == "John");
  assert( p.d!"father".d!"name".d!"length".get(0) == 4);
  assert( p.d!"father".d!"father".d!"name".d!"length".get(0) == 0);
  assert( (cast(Person) null).d!"father".d!"father".d!"father".get 
is null);


That is a "compact" version of a first solution using lambdas

  assert( 
dot(p).dot(a=>a.father).dot(a=>a.father).dot(a=>a.name).dot(a=>a.length).get(0)
== 0);

Find more details here:

https://run.dlang.io/gist/392c06e745d1a35df71084ce4d29fed7
Jan 13 2021
parent ddcovery <antoniocabreraperez gmail.com> writes:
On Wednesday, 13 January 2021 at 09:02:37 UTC, ddcovery wrote:

 Find more details here:

 https://run.dlang.io/gist/392c06e745d1a35df71084ce4d29fed7


Ups... it seems that the link is not working (it is the first 
time I try to generate a dalng/gist link... I'm not sure if this 
can really be done)...

I will create an example github project tonight... may be it can 
help you.
Jan 13 2021
prev sibling next sibling parent ddcovery <antoniocabreraperez gmail.com> writes:
On Tuesday, 12 January 2021 at 21:37:11 UTC, Jack wrote:

 I was looking for a way to avoid null checks everywhere. I was 
 checking the Null object pattern, or use something like enforce 
 pattern, or even if I could make a new operator and implement 


 actually), Kotlin also got something in this area[2]

 What some D ways to avoid those checks?

 [1]: 
 https://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000047.html
 [2]: 
 https://kotlinlang.org/docs/reference/null-safety.html#safe-calls


Hi Jack,

I have created this example implementation of the "Null safety" 
pattern using templates in D:

https://github.com/ddcovery/d_null_safety

It is, basically, a monad (functional programming orientation)  
with some syntax sugar taking advantage of the power of templates 
in D.
Jan 13 2021
prev sibling parent reply =?UTF-8?Q?Christian_K=c3=b6stlin?= <christian.koestlin gmail.com> writes:
On 12.01.21 22:37, Jack wrote:

 I was looking for a way to avoid null checks everywhere. I was checking 
 the Null object pattern, or use something like enforce pattern, or even 

 operator, that Java was going to have one but they refused[1] (doesn't 

 
 What some D ways to avoid those checks?
 
 [1]: 
 https://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000047.html
 [2]: https://kotlinlang.org/docs/reference/null-safety.html#safe-calls


Did you have a look at https://code.dlang.org/packages/optional?
Especially https://aliak00.github.io/optional/optional/oc/oc.html might 
go in the right direction.


Kind regards,
Christian
Jan 14 2021
parent ddcovery <antoniocabreraperez gmail.com> writes:
On Thursday, 14 January 2021 at 21:49:41 UTC, Christian Köstlin 
wrote:

 ...
 Did you have a look at https://code.dlang.org/packages/optional?
 Especially 
 https://aliak00.github.io/optional/optional/oc/oc.html might go 
 in the right direction.


 Kind regards,
 Christian


Thats nice!!!

I was commenting the need of a MayBe (some/none) monad compatible 
with Ranges (as an alternative to Nullable!T ) in  
https://forum.dlang.org/post/gxapatzfkoigcdhrdztv forum.dlang.org

Thanks a lot Christian.
Jan 14 2021