digitalmars.D - minimal evaluation

Qian Xu (17/17) Apr 06 2009 Hi All,

Qian Xu (2/9) Apr 06 2009 Update: If minimal evaluation is not always enabled, and foo.getBar is N...

davidl (5/15) Apr 06 2009 huh? post the whole code plz. It should work.

downs (4/27) Apr 06 2009 Short-circuit evaluation is always enabled.

Daniel Keep (4/34) Apr 06 2009 You beat me to it, AND you found it in the spec.

downs (4/41) Apr 06 2009 Ooh a cookie!

TomD (5/22) Apr 06 2009 Make it return true then. An "or" is true when it hits the first

downs (3/27) Apr 07 2009 .. Wait. Did I just read that right - when an argument is null, isNull ...

TomD (8/11) Apr 07 2009 At least that is what he had written. Seems to be a case of

Qian Xu <quian.xu stud.tu-ilmenau.de> writes:

Hi All,

Is minimal evaluation always enabled in D?

I want to write a function IsNull(), so that I can check the precondition as
follows:

  if (isNull(foo) ||
      isNull(foo.getBar) ||
      isNull(foo.getBar.getBar2)
  {
    return false;
  }
  // normal code goes here

If an argument is null, the IsNull() will return false. Internally it will
be logged to console as well.

But I am not sure, if dmd-compiler generates code without minimal evaluation
in some cases. If minimal evaluation is not always enabled. I cannot do
precodition check in my way. 

--Qian

Apr 06 2009

Qian Xu <quian.xu stud.tu-ilmenau.de> writes:

 
 if (isNull(foo) ||
     isNull(foo.getBar) ||
     isNull(foo.getBar.getBar2)
 {
   return false;
 }

Update: If minimal evaluation is not always enabled, and foo.getBar is NULL.
I will get a segfault when evaluating foo.getBar.getBar2.

Apr 06 2009

davidl <davidl nospam.org> writes:

�� Mon, 06 Apr 2009 19:33:31 +0800��Qian Xu <quian.xu stud.tu-ilmenau.de>  
д��:

 if (isNull(foo) ||
     isNull(foo.getBar) ||
     isNull(foo.getBar.getBar2)
 {
   return false;
 }

 Update: If minimal evaluation is not always enabled, and foo.getBar is  
 NULL.
 I will get a segfault when evaluating foo.getBar.getBar2.


huh? post the whole code plz. It should work.

-- 
ʹ�� Opera �����Եĵ����ʼ��ͻ�����: http://www.opera.com/mail/

Apr 06 2009

downs <default_357-line yahoo.de> writes:

Qian Xu wrote:
 Hi All,
 
 Is minimal evaluation always enabled in D?
 
 I want to write a function IsNull(), so that I can check the precondition as
 follows:
 
   if (isNull(foo) ||
       isNull(foo.getBar) ||
       isNull(foo.getBar.getBar2)
   {
     return false;
   }
   // normal code goes here
 
 If an argument is null, the IsNull() will return false. Internally it will
 be logged to console as well.
 
 But I am not sure, if dmd-compiler generates code without minimal evaluation
 in some cases. If minimal evaluation is not always enabled. I cannot do
 precodition check in my way. 
 
 --Qian

Short-circuit evaluation is always enabled.

http://digitalmars.com/d/1.0/expression.html#OrOrExpression

"If the left operand, converted to type bool, evaluates to true, then the right
operand is not evaluated."

Apr 06 2009

Daniel Keep <daniel.keep.lists gmail.com> writes:

downs wrote:
 Qian Xu wrote:
 Hi All,

 Is minimal evaluation always enabled in D?

 I want to write a function IsNull(), so that I can check the precondition as
 follows:

   if (isNull(foo) ||
       isNull(foo.getBar) ||
       isNull(foo.getBar.getBar2)
   {
     return false;
   }
   // normal code goes here

 If an argument is null, the IsNull() will return false. Internally it will
 be logged to console as well.

 But I am not sure, if dmd-compiler generates code without minimal evaluation
 in some cases. If minimal evaluation is not always enabled. I cannot do
 precodition check in my way. 

 --Qian

 
 Short-circuit evaluation is always enabled.
 
 http://digitalmars.com/d/1.0/expression.html#OrOrExpression
 
 "If the left operand, converted to type bool, evaluates to true, then the
right operand is not evaluated."

You beat me to it, AND you found it in the spec.

?cookie downs

  -- Daniel

Apr 06 2009

downs <default_357-line yahoo.de> writes:

Daniel Keep wrote:
 
 downs wrote:
 Qian Xu wrote:
 Hi All,

 Is minimal evaluation always enabled in D?

 I want to write a function IsNull(), so that I can check the precondition as
 follows:

   if (isNull(foo) ||
       isNull(foo.getBar) ||
       isNull(foo.getBar.getBar2)
   {
     return false;
   }
   // normal code goes here

 If an argument is null, the IsNull() will return false. Internally it will
 be logged to console as well.

 But I am not sure, if dmd-compiler generates code without minimal evaluation
 in some cases. If minimal evaluation is not always enabled. I cannot do
 precodition check in my way. 

 --Qian

 Short-circuit evaluation is always enabled.

 http://digitalmars.com/d/1.0/expression.html#OrOrExpression

 "If the left operand, converted to type bool, evaluates to true, then the
right operand is not evaluated."

 
 You beat me to it, AND you found it in the spec.
 
 ?cookie downs

Ooh a cookie!

:D

:munch:

 
   -- Daniel

Apr 06 2009

TomD <t_demmer nospam.web.de> writes:

Qian Xu Wrote:

 Hi All,
 
 Is minimal evaluation always enabled in D?
 
 I want to write a function IsNull(), so that I can check the precondition as
 follows:
 
   if (isNull(foo) ||
       isNull(foo.getBar) ||
       isNull(foo.getBar.getBar2)
   {
     return false;
   }
   // normal code goes here
 
 If an argument is null, the IsNull() will return false. Internally it will
 be logged to console as well.

Make it return true then. An "or" is true when it hits the first
true expression. 

Ciao
TomD

Apr 06 2009

downs <default_357-line yahoo.de> writes:

TomD wrote:
 Qian Xu Wrote:
 
 Hi All,

 Is minimal evaluation always enabled in D?

 I want to write a function IsNull(), so that I can check the precondition as
 follows:

 �  if (isNull(foo) ||
 �  �  �  isNull(foo.getBar) ||
 �  �  �  isNull(foo.getBar.getBar2)
 �  {
 �  �  return false;
 �  }
 �  // normal code goes here

 If an argument is null, the IsNull() will return false. Internally it will
 be logged to console as well.

 Make it return true then. An "or" is true when it hits the first
 true expression. 
 

 .. Wait. Did I just read that right - when an argument is null, isNull returns
*false*?

What the hell?

 Ciao
 TomD

Apr 07 2009

TomD <t_demmer nospam.web.de> writes:

downs Wrote:

[...]
  .. Wait. Did I just read that right - when an argument is null, isNull
returns *false*?
 
 What the hell?

At least that is what he had written. Seems to be a case of
"double negation is still a negation", an idiom quite common
here in Bavaria. Not in programming, though.

:-)

Ciao
TomD

Apr 07 2009

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