• Alex Burton <alexibu mac.com> Mar 05 2009
• Alex Burton <alexibu mac.com> Mar 05 2009
• Alex Burton <alexibu mac.com> Mar 05 2009
• Ary Borenszweig <ary esperanto.org.ar> Mar 05 2009
• Rainer Deyke <rainerd eldwood.com> Mar 05 2009

Alex Burton <alexibu mac.com> writes:

bearophile Wrote:

 Andrei Alexandrescu:
 I did some more research and found a study:
 http://users.encs.concordia.ca/~chalin/papers/TR-2006-003.v3s-pub.pdf
 ...
 Turns out in 2/3 of cases, references are really meant to be non-null... 
 not really a landslide but a comfortable majority.


 Thank you for bringing real data to this debate.
 Note that 2/3 is relative to nonlocal variables only:
 
In Java programs, at least 2/3 of declarations (other than local variables)
that are of 


 We exclude local variables because their non-nullity can be inferred by
intra-procedural 
 analysis<
 
 So the total percentage may be different (higher?).
 Anyway, nonnullable by default seems the way to go if such feature is added.
 



People are writing code that has a design intention of nullable (as shown in
the study) precisly because that is the default reference type in the language. 

Inferring that the default for a new language should be nullable based on these
statistics would be a logical error.

Implementing default non nullable would have the effect of reducing the amount
of design intentional nullable used. It would also greatly increase the quality
and maintainability of the code, as all references not specifically marked as
nullable could be safely dereferenced.

Alex

Alex Burton <alexibu mac.com> writes:

Alex Burton Wrote:

 bearophile Wrote:
 
 Andrei Alexandrescu:
 I did some more research and found a study:
 http://users.encs.concordia.ca/~chalin/papers/TR-2006-003.v3s-pub.pdf
 ...
 Turns out in 2/3 of cases, references are really meant to be non-null... 
 not really a landslide but a comfortable majority.


 Thank you for bringing real data to this debate.
 Note that 2/3 is relative to nonlocal variables only:
 
In Java programs, at least 2/3 of declarations (other than local variables)
that are of 


 We exclude local variables because their non-nullity can be inferred by
intra-procedural 
 analysis<
 
 So the total percentage may be different (higher?).
 Anyway, nonnullable by default seems the way to go if such feature is added.
 


 
 People are writing code that has a design intention of nullable (as shown in
the study) precisly because that is the default reference type in the language. 
 
 Inferring that the default for a new language should be nullable based on
these statistics would be a logical error.
 
 Implementing default non nullable would have the effect of reducing the amount
of design intentional nullable used. It would also greatly increase the quality
and maintainability of the code, as all references not specifically marked as
nullable could be safely dereferenced.
 
 Alex


Oops I'm wrong the 2/3 is NON nullable. My brain seems to have trouble reading
all this 'non null' stuff.

Alex Burton <alexibu mac.com> writes:

Alex Burton Wrote:


 
 Oops I'm wrong the 2/3 is NON nullable. My brain seems to have trouble reading
all this 'non null' stuff.
 



What we really want in the D language and the language of the discussions about
D is simple.

1) Types.

2) Nullable Types - optional

There is no need for Non Nullable types. These are Types.

Alex

Ary Borenszweig <ary esperanto.org.ar> writes:

Alex Burton escribió:
 Alex Burton Wrote:
 
 
 Oops I'm wrong the 2/3 is NON nullable. My brain seems to have trouble reading
all this 'non null' stuff.


 
 What we really want in the D language and the language of the discussions
about D is simple.
 
 1) Types.
 
 2) Nullable Types - optional
 
 There is no need for Non Nullable types. These are Types.


I think nullable types can't be optional. How do you implement a linked 
list without them? You use a dummy value for the "no next node"? Naaah...

 
 Alex

Rainer Deyke <rainerd eldwood.com> writes:

Ary Borenszweig wrote:
 I think nullable types can't be optional. How do you implement a linked
 list without them? You use a dummy value for the "no next node"? Naaah...


A nullable type is, conceptually, a container that can contain either
zero or one element.  If there was no language or library support for
nullable types, you could always use a dynamic array or some othet
container instead.


-- 
Rainer Deyke - rainerd eldwood.com