• Steve Jackson (13/13) Mar 05 2008 (This is a report of what I believe is a "new" bug in the D compiler. I...
• Robert Fraser (10/29) Mar 05 2008 Hi Steve,
• Simen Kjaeraas (6/15) Mar 05 2008 Actually, "hello world" is indeed correct output, as the scope(exit) is ...
• Gide Nwawudu (5/18) Mar 06 2008 Looks similar to this bug.
• Max Samukha (8/21) Mar 06 2008 Looks like a bug but makes no sense in a real application anyway?
• Janice Caron (9/12) Mar 06 2008 For that matter,
• Max Samukha (42/55) Mar 06 2008 scope is redundant in your example because it is the only statement
• Max Samukha (5/67) Mar 06 2008 Sorry, Janice, somehow my brain mistook you for Steve.
• Steve Jackson (3/4) Mar 06 2008 No. I encountered this while experimenting with the behavior of scope()...
• Robert Fraser (4/34) Mar 06 2008 Compile-time values could evaluate to true, and compile-time code
• Max Samukha (20/24) Mar 07 2008 You are right, this is a problem.

Steve Jackson <sjackso cs.wisc.edu> writes:

(This is a report of what I believe is a "new" bug in the D compiler.  I'm not
sure whether this newsgroup is the appropriate place to report such things, but
it is the best I have been able to find.)

While experimenting with scope guard statements, I came across some unexpected
behavior.  This snippet:

{
 if( true ){ scope(exit) writef("hello"); }
 writefln(" world" );
}

Produces the output "hello world", as I expected.  However, if I remove the if
statement's braces, like so:

{
 if( true ) scope(exit) writef("hello");
 writefln( " world" );
}

... then the first writef call is skipped entirely, and the output is " world".
 No errors or compiler warnings are generated.

I'm using the dmd compiler v2.010 on Linux.

Robert Fraser <fraserofthenight gmail.com> writes:

Hi Steve,

The place to report issues is here: http://d.puremagic.com/issues/ . You 
need to register a bugzilla account, then click "New" on the bottom bar, 
then "D", and enter a world of happiness and bug reporting.

I would guess that in both cases, that should produce the output:

  world
hello

Since the writefln("hello") is within a scope-exit, so should only fire 
as part of the function exit condition.

Steve Jackson wrote:
 (This is a report of what I believe is a "new" bug in the D compiler.  I'm not
sure whether this newsgroup is the appropriate place to report such things, but
it is the best I have been able to find.)
 
 While experimenting with scope guard statements, I came across some unexpected
behavior.  This snippet:
 
 {
  if( true ){ scope(exit) writef("hello"); }
  writefln(" world" );
 }
 
 Produces the output "hello world", as I expected.  However, if I remove the if
statement's braces, like so:
 
 {
  if( true ) scope(exit) writef("hello");
  writefln( " world" );
 }
 
 ... then the first writef call is skipped entirely, and the output is "
world".  No errors or compiler warnings are generated.
 
 I'm using the dmd compiler v2.010 on Linux.

"Simen Kjaeraas" <simen.kjaras gmail.com> writes:

On Wed, 05 Mar 2008 23:54:35 +0100, Robert Fraser  
<fraserofthenight gmail.com> wrote:

 Hi Steve,

 The place to report issues is here: http://d.puremagic.com/issues/ . You  
 need to register a bugzilla account, then click "New" on the bottom bar,  
 then "D", and enter a world of happiness and bug reporting.

 I would guess that in both cases, that should produce the output:

   world
 hello

 Since the writefln("hello") is within a scope-exit, so should only fire  
 as part of the function exit condition.

Actually, "hello world" is indeed correct output, as the scope(exit) is  
executed when it exits the scope of the if{}.

The latter does indeed look like a bug, though.

-- Simen

Gide Nwawudu <gide btinternet.com> writes:

On Wed, 05 Mar 2008 16:26:27 -0500, Steve Jackson
<sjackso cs.wisc.edu> wrote:

(This is a report of what I believe is a "new" bug in the D compiler.  I'm not
sure whether this newsgroup is the appropriate place to report such things, but
it is the best I have been able to find.)

While experimenting with scope guard statements, I came across some unexpected
behavior.  This snippet:

{
 if( true ){ scope(exit) writef("hello"); }
 writefln(" world" );
}

Produces the output "hello world", as I expected.  However, if I remove the if
statement's braces, like so:

{
 if( true ) scope(exit) writef("hello");
 writefln( " world" );
}

... then the first writef call is skipped entirely, and the output is " world".
 No errors or compiler warnings are generated.

I'm using the dmd compiler v2.010 on Linux.

Looks similar to this bug.

http://d.puremagic.com/issues/show_bug.cgi?id=1765

Gide

Max Samukha <samukha voliacable.com.removethis> writes:

On Wed, 05 Mar 2008 16:26:27 -0500, Steve Jackson
<sjackso cs.wisc.edu> wrote:

(This is a report of what I believe is a "new" bug in the D compiler.  I'm not
sure whether this newsgroup is the appropriate place to report such things, but
it is the best I have been able to find.)

While experimenting with scope guard statements, I came across some unexpected
behavior.  This snippet:

{
 if( true ){ scope(exit) writef("hello"); }
 writefln(" world" );
}

Produces the output "hello world", as I expected.  However, if I remove the if
statement's braces, like so:

{
 if( true ) scope(exit) writef("hello");
 writefln( " world" );
}

... then the first writef call is skipped entirely, and the output is " world".
 No errors or compiler warnings are generated.

I'm using the dmd compiler v2.010 on Linux.

Looks like a bug but makes no sense in a real application anyway?

if( true ) scope(exit) writef("hello");
is semantically the same as simply
if( true ) writef("hello");

Do you have any use case for that?
 

"Janice Caron" <caron800 googlemail.com> writes:

On 06/03/2008, Max Samukha <samukha voliacable.com.removethis> wrote:
  if( true ) scope(exit) writef("hello");

 is semantically the same as simply
  if( true ) writef("hello");

For that matter,

    if (true) anything

is the same as

    anything

But I assume "if (condition)" what what was really intended. It seems
to me that one could instead write:

    scope(exit) { if (condition) writef("hello") }

That is, reverse the order of "scope" and "if".

Max Samukha <samukha voliacable.com.removethis> writes:

On Thu, 6 Mar 2008 10:47:19 +0000, "Janice Caron"
<caron800 googlemail.com> wrote:

On 06/03/2008, Max Samukha <samukha voliacable.com.removethis> wrote:
  if( true ) scope(exit) writef("hello");

 is semantically the same as simply
  if( true ) writef("hello");

For that matter,

    if (true) anything

is the same as

    anything

scope is redundant in your example because it is the only statement
within if's scope. It executes a block of statements when the thread
exits if's scope. you could as well omit it.

if (condition)
{
    scope(exit)
   {
		...
   }
}

or without braces (according to you, doesn't work as expected)

if (condition)
    scope(exit)
    {
		...
    }

should be equivalent to

if (condition)
{
	...
}

In case of static if, which doesn't create a new scope:

{
    static if (condition)
       scope (exit)
            writef("hello");

} // hello should be printed when control gets here (not tested)

But I assume "if (condition)" what what was really intended. It seems
to me that one could instead write:

    scope(exit) { if (condition) writef("hello") }

That is, reverse the order of "scope" and "if".

{
    bool condition = ...
	
    ...
	
    scope(exit)
    { 
        if (condition) writef("hello");
    }

  ...	
} // hello is printed at this point if condition is true
  // and the function didn't return or throw before
  // the 'scope'

Max Samukha <samukha voliacable.com.removethis> writes:

On Thu, 06 Mar 2008 15:37:07 +0200, Max Samukha
<samukha voliacable.com.removethis> wrote:

On Thu, 6 Mar 2008 10:47:19 +0000, "Janice Caron"
<caron800 googlemail.com> wrote:

On 06/03/2008, Max Samukha <samukha voliacable.com.removethis> wrote:
  if( true ) scope(exit) writef("hello");

 is semantically the same as simply
  if( true ) writef("hello");

For that matter,

    if (true) anything

is the same as

    anything

scope is redundant in your example because it is the only statement
within if's scope. It executes a block of statements when the thread
exits if's scope. you could as well omit it.

if (condition)
{
    scope(exit)
   {
		...
   }
}

or without braces (according to you, doesn't work as expected)

if (condition)
    scope(exit)
    {
		...
    }

should be equivalent to

if (condition)
{
	...
}

In case of static if, which doesn't create a new scope:

{
    static if (condition)
       scope (exit)
            writef("hello");

} // hello should be printed when control gets here (not tested)

But I assume "if (condition)" what what was really intended. It seems
to me that one could instead write:

    scope(exit) { if (condition) writef("hello") }

That is, reverse the order of "scope" and "if".

{
    bool condition = ...
	
    ...
	
    scope(exit)
    { 
        if (condition) writef("hello");
    }

  ...	
} // hello is printed at this point if condition is true
  // and the function didn't return or throw before
  // the 'scope'

Sorry, Janice, somehow my brain mistook you for Steve.
Please ignore
  

Steve Jackson <sjackso cs.wisc.edu> writes:

Max Samukha Wrote:
 Do you have any use case for that?

No.  I encountered this while experimenting with the behavior of scope(), not
while building any particular application.  I agree that my example is a corner
case.  But I thought it best to raise the issue in case it reflects some more
subtle problem in the compiler.

I appreciate the prompt responses! 

Robert Fraser <fraserofthenight gmail.com> writes:

Max Samukha wrote:
 On Wed, 05 Mar 2008 16:26:27 -0500, Steve Jackson
 <sjackso cs.wisc.edu> wrote:
 
 (This is a report of what I believe is a "new" bug in the D compiler.  I'm not
sure whether this newsgroup is the appropriate place to report such things, but
it is the best I have been able to find.)

 While experimenting with scope guard statements, I came across some unexpected
behavior.  This snippet:

 {
 if( true ){ scope(exit) writef("hello"); }
 writefln(" world" );
 }

 Produces the output "hello world", as I expected.  However, if I remove the if
statement's braces, like so:

 {
 if( true ) scope(exit) writef("hello");
 writefln( " world" );
 }

 ... then the first writef call is skipped entirely, and the output is "
world".  No errors or compiler warnings are generated.

 I'm using the dmd compiler v2.010 on Linux.

 
 Looks like a bug but makes no sense in a real application anyway?
 
 if( true ) scope(exit) writef("hello");
 is semantically the same as simply
 if( true ) writef("hello");
 
 Do you have any use case for that?

Compile-time values could evaluate to true, and compile-time code 
generation could very easily create code that would seem silly to write 
directly. So it's a valid problem.

Max Samukha <maxsamukha gmail.com> writes:

Robert Fraser wrote:

 
 Compile-time values could evaluate to true, and compile-time code
 generation could very easily create code that would seem silly to write
 directly. So it's a valid problem.

You are right, this is a problem.

Interestingly, mixing in the ThenStatement works fine:

----
if (true)
    mixin ("scope(exit) Stdout(\"hello \").newline;");
// prints hello as expected.
----

I guess, this is because a string mixin creates a new scope, which is a bug
(or a feature? The specification is not specific on that):

----
mixin ("scope(exit) Stdout(\"Exiting scope.\").newline;");
Stdout("After mixin").newline;
----

outputs:
Exiting mixin scope.
After mixin

while I would expect the reverse.