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digitalmars.D.learn - Implicit fall through not detected (Example from lex.html)

reply "Andre" <andre s-e-a-p.de> writes:
Hi,

I am little bit confused. I am copied the switch example from 
lex.html
and expected that case 6 will lead to a syntax error due to the 
missing
break statement. But the example compiles without error (C:>dmd 
app)

I tried 3 different dmd version, also the newest beta.

Kind regards
André

import std.stdio: writeln;

void main()
{

int number;
string message;

switch (number)
{
   default:    // valid
	throw new Exception("unknown number");

   case 3:     // valid
	message ~= "three ";
	break;

   case 5:     // valid
	message ~= "five ";
	goto case;

   case 6:     // ERROR: implicit fall-through
	message ~= "six ";

   case 1:     // valid
   case 2:     // valid
	message = "one or two";
}

}
Mar 02 2015
next sibling parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/02/2015 10:58 PM, Andre wrote:

 Hi,

 I am little bit confused. I am copied the switch example from lex.html
 and expected that case 6 will lead to a syntax error due to the missing
 break statement. But the example compiles without error (C:>dmd app)

 I tried 3 different dmd version, also the newest beta.

 Kind regards
 André

 import std.stdio: writeln;

 void main()
 {

 int number;
 string message;

 switch (number)
 {
    default:    // valid
      throw new Exception("unknown number");

    case 3:     // valid
      message ~= "three ";
      break;

    case 5:     // valid
      message ~= "five ";
      goto case;

    case 6:     // ERROR: implicit fall-through
      message ~= "six ";

    case 1:     // valid
    case 2:     // valid
      message = "one or two";
 }

 }


Compile with -w command line switch. :)

Ali
Mar 02 2015
prev sibling parent reply ketmar <ketmar ketmar.no-ip.org> writes:
On Tue, 03 Mar 2015 06:58:14 +0000, Andre wrote:


 Hi,
=20
 I am little bit confused. I am copied the switch example from lex.html
 and expected that case 6 will lead to a syntax error due to the missing
 break statement. But the example compiles without error (C:>dmd app)


implicit fallthru is not a fatal bug (but i believe it should be), it=20
generates only warning.=
Mar 02 2015
parent reply "Andre" <andre s-e-a-p.de> writes:
On Tuesday, 3 March 2015 at 07:27:33 UTC, ketmar wrote:

 implicit fallthru is not a fatal bug (but i believe it should 
 be), it
 generates only warning.


I am also not really happy with the actual behavor (w / wi switch 
needed) because the documentation is clear about that it is an 
error:

-- from language reference:
A ScopeStatementList must either be empty, or be ended with a 
ContinueStatement, BreakStatement, ReturnStatement, 
GotoStatement, ThrowStatement or assert(0) expression unless this 
is the last case. This is to set apart with C's error-prone 
implicit fall-through behavior. goto case; could be used for 
explicit fall-through
--

Fortunately dub is using the correct switches by default

Kind regards
André
Mar 03 2015
parent "bearophile" <bearophileHUGS lycos.com> writes:
Andre:


 I am also not really happy with the actual behavor (w / wi 
 switch needed)


You shall always compile your D code with warnings active, unless 
you need them disabled for some real reason.

Eventually the fall through warning will become a deprecation and 
then an error. It's meant to be an error, but in D we introduce 
errors slowly.

Bye,
bearophile
Mar 03 2015