Thread overview
[Issue 1118] New: weird switch statement behaviour
Apr 09, 2007
d-bugmail
Apr 09, 2007
d-bugmail
Apr 09, 2007
Manuel König
Apr 09, 2007
d-bugmail
Apr 10, 2007
Manuel König
Jul 01, 2007
d-bugmail
April 09, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=1118

           Summary: weird switch statement behaviour
           Product: D
           Version: 1.010
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: accepts-invalid, spec
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: manuelk89@gmx.net


The documentation for the switch statement says:

    SwitchStatement:
            switch ( Expression ) ScopeStatement

So there must not be 'case', 'default' or scoping brackets after the switch. Hence this would be valid code (and actually compiles, throwing a 'Switch Default' error for the first example):

        switch (1)
                for (int i=0; i<5; i++) writefln(i);

        // another, yet acceptable but ugly looking example example
        switch (true)
        case true:  writefln("foo");

        switch (5)
        {
                // do anything but no switch/case
                writefln("foo");
        }

But beside a ScopeStatement, even a normal Statement gets accepted by the compiler (at least I could not figure out a transition from a ScopeStatement to an ExpressionStatement):

    switch(2)
        writefln("foo");


_________________________________________________________________
Examples were tested on Ubuntu Linux with
    * dmd 1.010
    * gdc 0.23

_________________________________________________________________ PS: I think a definition like this would do the job:

    SwitchStatement:
            switch ( Expression ) { SwitchItemList }

    SwitchItemList:
            SwitchItem
            SwitchItem SwitchItemList

    SwitchItem:
            CaseStatement
            DefaultStatement


-- 

April 09, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=1118


shro8822@uidaho.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |shro8822@uidaho.edu




------- Comment #1 from shro8822@uidaho.edu  2007-04-09 18:06 -------
What about cases like this:

switch(i)
{
 while(i)
 {
  foo();
  case 0: bar();
  case 1: baz();
  case 3: i--;
 }
}


-- 

April 09, 2007
> What about cases like this:
> 
> switch(i)
> {
>  while(i)
>  {
>   foo();
>   case 0: bar();
>   case 1: baz();
>   case 3: i--;
>  }
> }
> 
> 

Nice idea, never had to use it that way. Think this issue should be tagged as INVALID...

But looking at the examples given before, it would be nice if the compiler would give at least a warning about missing switch labels.
April 09, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=1118





------- Comment #3 from shro8822@uidaho.edu  2007-04-09 18:41 -------
Not having a case might not be a problem: tuples can be foreached to generate cases and a zero length tuple might be valid. You would however expect their to be a default in that case.

int Foo(A...)(int i)
{
 switch(i)
 {
  default:
   // code
   break;
  foreach(a;A)
  {
   case a:
    // code
    // break;
  }
 }
}


-- 

April 10, 2007
> ------- Comment #3 from shro8822@uidaho.edu  2007-04-09 18:41 -------
> Not having a case might not be a problem: tuples can be foreached to generate
> cases and a zero length tuple might be valid. You would however expect their to
> be a default in that case.
> 
> int Foo(A...)(int i)
> {
>  switch(i)
>  {
>   default:
>    // code
>    break;
>   foreach(a;A)
>   {
>    case a:
>     // code
>     // break;
>   }
>  }
> }
> 
> 

Wow, again I'm amazed by D's features! But I could not compile your code (yet a real bug :P ). But I could find a workaround:

import std.stdio;

// your version (should work, but it doesn't)
void Foo1(A...)(int i)
{
	switch (i)
	{
		foreach(a; A)
		{
		case a:		// line 9
			writefln(a);
		}
	}
}

// workaround (does exactly the same thing, but with more clumsy code)
void Foo2(A...)(int i)
{
	switch (i)
	{
		foreach(j, a; A)
		{
		case A[j]:
			writefln(a);
		}
	}
}

void main()
{
	//Foo1!(1,2,3,4,5)(1); // line 29
	Foo2!(1,2,3,4,5)(1);
}

The output is
1
2
3
4
5
just as expected. But uncommenting Foo1 gives an error. Error log from Code::Blocks:

hello.d:9: Error: case must be a string or an integral constant, not a
hello.d:9: Error: case must be a string or an integral constant, not a
hello.d:9: Error: duplicate case 0 in switch statement
hello.d:9: Error: case must be a string or an integral constant, not a
hello.d:9: Error: duplicate case 0 in switch statement
hello.d:9: Error: case must be a string or an integral constant, not a
hello.d:9: Error: duplicate case 0 in switch statement
hello.d:9: Error: case must be a string or an integral constant, not a
hello.d:9: Error: duplicate case 0 in switch statement
hello.d:29: template instance hello.Foo1!(1,2,3,4,5) error instantiating
:: === Build finished: 10 errors, 0 warnings ===

I think that's worth a bug report.
July 01, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=1118


bugzilla@digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED




------- Comment #5 from bugzilla@digitalmars.com  2007-07-01 13:29 -------
Fixed DMD 1.018 and DMD 2.002


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