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digitalmars.D - Default value of class

reply "David B. Held" <dheld codelogicconsulting.com> writes:
Can anyone tell me the expected runtime behavior of this program?

class Foo
{ }

void main()
{
     Foo foo;
     assert(foo == null);
}

It's certainly not what I expected, and I want to know if I should file 
a bug report or not.

Dave
May 19 2007
parent reply Dave <Dave_member pathlink.com> writes:
David B. Held wrote:

 Can anyone tell me the expected runtime behavior of this program?
 
 class Foo
 { }
 
 void main()
 {
     Foo foo;
     assert(foo == null);
 }
 
 It's certainly not what I expected, and I want to know if I should file 
 a bug report or not.
 
 Dave


Try 'assert(foo is null);'
May 19 2007
parent reply davidb <ta-nospam-zz gmx.at> writes:
Dave schrieb:

 David B. Held wrote:

 Can anyone tell me the expected runtime behavior of this program?

 class Foo
 { }

 void main()
 {
     Foo foo;
     assert(foo == null);
 }

 It's certainly not what I expected, and I want to know if I should 
 file a bug report or not.

 Dave


 
 Try 'assert(foo is null);'


See http://www.digitalmars.com/d/operatoroverloading.html


 Note: Comparing a reference to a class object against null  should be 
 done as:

 if (a is null)


 and not as:

 if (a == null)


 The latter is converted to:

 if (a.opEquals(null))




which will fail if a is null because it can't use it to reference to 
opEquals()

david
May 20 2007
parent reply "David B. Held" <dheld codelogicconsulting.com> writes:
davidb wrote:

 Dave schrieb:

 David B. Held wrote:

 Can anyone tell me the expected runtime behavior of this program?

 class Foo
 { }

 void main()
 {
     Foo foo;
     assert(foo == null);
 }

 It's certainly not what I expected, and I want to know if I should 
 file a bug report or not.

 Dave


 Try 'assert(foo is null);'


 
 See http://www.digitalmars.com/d/operatoroverloading.html
 
  > Note: Comparing a reference to a class object against null  should be 
  > done as:
  >> if (a is null)
  > and not as:
  >> if (a == null)
  > The latter is converted to:
  >> if (a.opEquals(null))
 
 which will fail if a is null because it can't use it to reference to 
 opEquals()


Aha...thanks guys.  However, I am disturbed by two things: 1) that this 
looks more like VB than C++ ;), and 2) that everyone in this thread is 
named "David".  Hmm...

Dave
May 20 2007
next sibling parent Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
David B. Held wrote:

 davidb wrote:

 Dave schrieb:

 David B. Held wrote:

 Can anyone tell me the expected runtime behavior of this program?

 class Foo
 { }

 void main()
 {
     Foo foo;
     assert(foo == null);
 }

 It's certainly not what I expected, and I want to know if I should 
 file a bug report or not.

 Dave


 Try 'assert(foo is null);'


 See http://www.digitalmars.com/d/operatoroverloading.html

  > Note: Comparing a reference to a class object against null  should 
 be  > done as:
  >> if (a is null)
  > and not as:
  >> if (a == null)
  > The latter is converted to:
  >> if (a.opEquals(null))

 which will fail if a is null because it can't use it to reference to 
 opEquals()


 
 Aha...thanks guys.  However, I am disturbed by two things: 1) that this 
 looks more like VB than C++ ;), and 2) that everyone in this thread is 
 named "David".  Hmm...
 
 Dave


o_O  It only makes sense though, for a language named "D".

We have our army of Davids, and the (Ch|K)ris's... at least there's just one
Walter. 
Could you imagine...

-- Chris (!) Nicholson-Sauls
May 20 2007
prev sibling parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"David B. Held" <dheld codelogicconsulting.com> wrote in message 
news:f2ptar$2022$1 digitalmars.com...

 this looks more like VB than C++


Well, maybe VB got some things right ;)
May 20 2007
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
Jarrett Billingsley wrote:

 "David B. Held" <dheld codelogicconsulting.com> wrote in message 
 news:f2ptar$2022$1 digitalmars.com...

 this looks more like VB than C++


 
 Well, maybe VB got some things right ;) 


It's still the only language I've seen that lets me pass temporaries and
literals as reference arguments... :)

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

http://xkcd.com/

v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP  http://hackerkey.com/
May 20 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Daniel Keep" <daniel.keep.lists gmail.com> wrote in message 
news:f2qf8m$2v85$1 digitalmars.com...

 Jarrett Billingsley wrote:

 "David B. Held" <dheld codelogicconsulting.com> wrote in message
 news:f2ptar$2022$1 digitalmars.com...

 this looks more like VB than C++


 Well, maybe VB got some things right ;)


 It's still the only language I've seen that lets me pass temporaries and
 literals as reference arguments... :)


Doesn't C++ have those ... && reference arguments?  Like int&& ?  You can 
pass temps to those.  Well I guess those are in C++09, so they're not part 
of the language yet.
May 20 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message 
news:f2qgao$3176$1 digitalmars.com...

 Doesn't C++ have those ... && reference arguments?  Like int&& ?  You can 
 pass temps to those.  Well I guess those are in C++09, so they're not part 
 of the language yet.


Though D can do this:

struct S
{
    int x;

    static S opCall(int x)
    {
        S s;
        s.x = x;
        return s;
    }
}

void foo(ref S s)
{
    writefln(s.x);
}

void main()
{
    foo(S(4));
}

Which I guess is pretty close.
May 20 2007
parent Daniel Keep <daniel.keep.lists gmail.com> writes:
Jarrett Billingsley wrote:

 "Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message 
 news:f2qgao$3176$1 digitalmars.com...

 Doesn't C++ have those ... && reference arguments?  Like int&& ?  You can 
 pass temps to those.  Well I guess those are in C++09, so they're not part 
 of the language yet.


 
 Though D can do this:
 
 struct S
 {
     int x;
 
     static S opCall(int x)
     {
         S s;
         s.x = x;
         return s;
     }
 }
 
 void foo(ref S s)
 {
     writefln(s.x);
 }
 
 void main()
 {
     foo(S(4));
 }
 
 Which I guess is pretty close. 


That's interesting; could that be NVRO?  That said, this still doesn't
work...


 import std.stdio;

 void foo(ref int a)
 {
     writefln("a: %s", a);
 }

 void main()
 {
     foo(42);
 }


H:\WINDOWS\system32\cmd.exe /c bud -clean -exec refargs
refargs.d(11): Error: constant 42 is not an lvalue

:(

This is a pain because I discovered that using ref arguments for my
vector library can net me a *big* speed increase, even more so once I
put in SSE optimisations.

The problem is that if I can't pass literals or temporaries, then it'll
render the library much harder to use.  Then again, maybe since the
vectors are structs, the above will work... need to give that a shot
when I'm not so busy.

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

http://xkcd.com/

v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP  http://hackerkey.com/
May 20 2007