www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.bugs - [Issue 1118] New: weird switch statement behaviour

reply d-bugmail puremagic.com writes:
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


--
Apr 09 2007
next sibling parent reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=1118


shro8822 uidaho.edu changed:

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





What about cases like this:

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


--
Apr 09 2007
parent =?ISO-8859-1?Q?Manuel_K=F6nig?= <ManuelK89 gmx.net> writes:
 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.
Apr 09 2007
prev sibling next sibling parent reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=1118






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;
  }
 }
}


--
Apr 09 2007
parent =?ISO-8859-1?Q?Manuel_K=F6nig?= <ManuelK89 gmx.net> writes:

 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.
Apr 09 2007
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=1118


bugzilla digitalmars.com changed:

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





Fixed DMD 1.018 and DMD 2.002


--
Jul 01 2007