• icee (24/24) Sep 10 2006 In http://www.digitalmars.com/d/expression.html, you said
• Stewart Gordon (17/33) Sep 11 2006 Do you mean:
• Ivan Senji (3/33) Sep 11 2006 That is a leftover from implicit conversions of expressions (null in
• icee (3/3) Sep 11 2006 So either the doc or the dmd should be fixed.

icee <iceelyne gmail.com> writes:

In http://www.digitalmars.com/d/expression.html, you said
"A null is implicitly converted to a Type delegate() by creating an
anonymous delegate that returns null."

But the truth seems not:

//char[] delegate () dg = null; //cause av
char[] delegate () dg = delegate char[]() {return null;};
try{dg();}catch(Exception e){writefln(e.msg);}

or, if i made any mistakes here?


null
The keyword null represents the null pointer value; technically it is of
type (void *). It can be implicitly cast to any pointer type, including
pointers to functions. The integer 0 cannot be cast to the null pointer.
Nulls are also used for empty arrays.

A null is implicitly converted to a Type delegate() by creating an anonymous
delegate that returns null. To get an actual null value for the delegate,
use one of the following:

const Type delegate() dgnull;   // default initializer for delegate is null
...
Type delegate() dg1;  // default initializer for delegate is null
Type delegate() dg2 = dgnull;
Type delegate() dg3 = (Type delegate()).init;
Type delegate() dg4 = cast(Type delegate()) null;

Type delegate() dg5 = null;  // initializes dg5 to
                             // delegate Type() { return null; }

Stewart Gordon <smjg_1998 yahoo.com> writes:

icee wrote:
 In http://www.digitalmars.com/d/expression.html, you said
 "A null is implicitly converted to a Type delegate() by creating an
 anonymous delegate that returns null."
 
 But the truth seems not:
 
 //char[] delegate () dg = null; //cause av

Do you mean:
(a) that merely assigning null to a delegate variable causes an AV?
(b) that calling dg afterwards causes an AV?

(a) certainly shouldn't be happening.  But if (b), of course it does. 
What else would it do?

<snip>
 const Type delegate() dgnull;   // default initializer for delegate is null
 ....
 Type delegate() dg1;  // default initializer for delegate is null
 Type delegate() dg2 = dgnull;
 Type delegate() dg3 = (Type delegate()).init;
 Type delegate() dg4 = cast(Type delegate()) null;
 
 Type delegate() dg5 = null;  // initializes dg5 to
                              // delegate Type() { return null; }

Case dg5 is certainly weird.

Stewart.

-- 
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GCS/M d- s:-  C++  a->--- UB  P+ L E  W++  N+++ o K-  w++  O? M V? PS- 
PE- Y? PGP- t- 5? X? R b DI? D G e++++ h-- r-- !y
------END GEEK CODE BLOCK------

My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.

Ivan Senji <ivan.senji_REMOVE_ _THIS__gmail.com> writes:

Stewart Gordon wrote:
 icee wrote:
 In http://www.digitalmars.com/d/expression.html, you said
 "A null is implicitly converted to a Type delegate() by creating an
 anonymous delegate that returns null."

 But the truth seems not:

 //char[] delegate () dg = null; //cause av

 
 Do you mean:
 (a) that merely assigning null to a delegate variable causes an AV?
 (b) that calling dg afterwards causes an AV?
 
 (a) certainly shouldn't be happening.  But if (b), of course it does. 
 What else would it do?
 
 <snip>
 const Type delegate() dgnull;   // default initializer for delegate is 
 null
 ....
 Type delegate() dg1;  // default initializer for delegate is null
 Type delegate() dg2 = dgnull;
 Type delegate() dg3 = (Type delegate()).init;
 Type delegate() dg4 = cast(Type delegate()) null;

 Type delegate() dg5 = null;  // initializes dg5 to
                              // delegate Type() { return null; }

 
 Case dg5 is certainly weird.
 

That is a leftover from implicit conversions of expressions (null in 
this case) to delegates, it shouldn't be a problem any more.

icee <iceelyne gmail.com> writes:

So either the doc or the dmd should be fixed.
Maybe the doc cos' implicit anonymous delegate creation for null is not very
useful.