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digitalmars.D.learn - shouldn't this code at least trigger a warning?

reply ketmar <ketmar ketmar.no-ip.org> writes:
subj. the code:

  void main () {
    import std.stdio;
    char ch =3D '!';
    switch (ch) {
      int n =3D 42;
      case '!': writeln(n, ": wow!"); break;
      default:
    }
  }


i think that such abomination should:
1. be forbidden, or
2. trigger a warning, or
3. execute initializer anyway.

currently the code is allowed, no warnings triggered, yet `n` is=20
uninitialized. and having uninitialized variable without "=3Dvoid" "should=20
not be".=
Apr 28 2015
next sibling parent reply "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Wednesday, 29 April 2015 at 06:37:44 UTC, ketmar wrote:

 subj. the code:

   void main () {
     import std.stdio;
     char ch = '!';
     switch (ch) {
       int n = 42;
       case '!': writeln(n, ": wow!"); break;
       default:
     }
   }


 i think that such abomination should:
 1. be forbidden, or
 2. trigger a warning, or
 3. execute initializer anyway.

 currently the code is allowed, no warnings triggered, yet `n` is
 uninitialized. and having uninitialized variable without 
 "=void" "should
 not be".


Agreed, this should be an error. Variables declared in one case 
block aren't even visible in other case blocks, this was probably 
an oversight.
Apr 29 2015
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 4/29/15 5:25 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net>" 
wrote:

 On Wednesday, 29 April 2015 at 06:37:44 UTC, ketmar wrote:

 subj. the code:

   void main () {
     import std.stdio;
     char ch = '!';
     switch (ch) {
       int n = 42;
       case '!': writeln(n, ": wow!"); break;
       default:
     }
   }


 i think that such abomination should:
 1. be forbidden, or
 2. trigger a warning, or
 3. execute initializer anyway.

 currently the code is allowed, no warnings triggered, yet `n` is
 uninitialized. and having uninitialized variable without "=void" "should
 not be".


 Agreed, this should be an error. Variables declared in one case block
 aren't even visible in other case blocks, this was probably an oversight.


I thought they were? A switch scope is just like a normal scope, but 
with a bunch of labels.

They should be visible in all *trailing* case blocks, since the rule is 
that your code that uses it must come after the declaration.

I agree the above should not be allowed. It's clear the compiler can 
detect a situation where n is used but not initialized.

-Steve
Apr 29 2015
prev sibling next sibling parent reply "Gary Willoughby" <dev nomad.so> writes:
On Wednesday, 29 April 2015 at 06:37:44 UTC, ketmar wrote:

 subj. the code:

   void main () {
     import std.stdio;
     char ch = '!';
     switch (ch) {
       int n = 42;
       case '!': writeln(n, ": wow!"); break;
       default:
     }
   }


 i think that such abomination should:
 1. be forbidden, or
 2. trigger a warning, or
 3. execute initializer anyway.

 currently the code is allowed, no warnings triggered, yet `n` is
 uninitialized. and having uninitialized variable without 
 "=void" "should
 not be".


Please raise an issue in bugzilla. This is obviously an error.
Apr 29 2015
parent ketmar <ketmar ketmar.no-ip.org> writes:
On Wed, 29 Apr 2015 10:48:36 +0000, Gary Willoughby wrote:


 Please raise an issue in bugzilla. This is obviously an error.


done: https://issues.dlang.org/show_bug.cgi?id=3D14532=
Apr 30 2015
prev sibling parent reply "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Wed, Apr 29, 2015 at 06:37:44AM +0000, ketmar via Digitalmars-d-learn wrote:

 subj. the code:
 
   void main () {
     import std.stdio;
     char ch = '!';
     switch (ch) {
       int n = 42;
       case '!': writeln(n, ": wow!"); break;
       default:
     }
   }
 
 
 i think that such abomination should:
 1. be forbidden, or
 2. trigger a warning, or
 3. execute initializer anyway.
 
 currently the code is allowed, no warnings triggered, yet `n` is
 uninitialized. and having uninitialized variable without "=void"
 "should not be".


Switch statements in D allow all sorts of abominations, if only you
would try it. I think it was originally designed to support a particular
loop idiom (sorry I forgot what it was called, and don't have time to
look it up right now), but in the process this also opened the door to
all sorts of nasty infelicities that probably breaks the type system,
control flow, and many other things. Basically, the block inside a
switch statement essentially amounts to free-for-all spaghetti code
where you're free to jump around case labels willy-nilly, declare
variables and jump over their initializations, break out of loops with
goto case, or enter into the middle of a loop, and all sorts of other
crazy things that, ostensibly, you shouldn't be able to do in a language
like D.


T

-- 
Let's eat some disquits while we format the biskettes.
Apr 29 2015
next sibling parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 04/29/2015 07:57 AM, H. S. Teoh via Digitalmars-d-learn wrote:


 Switch statements in D allow all sorts of abominations, if only you
 would try it. I think it was originally designed to support a particular
 loop idiom (sorry I forgot what it was called


   http://en.wikipedia.org/wiki/Duff%27s_device

Ali
Apr 29 2015
prev sibling parent ketmar <ketmar ketmar.no-ip.org> writes:
On Wed, 29 Apr 2015 07:57:07 -0700, H. S. Teoh via Digitalmars-d-learn
wrote:


 Switch statements in D allow all sorts of abominations, if only you
 would try it. I think it was originally designed to support a particular
 loop idiom (sorry I forgot what it was called, and don't have time to
 look it up right now), but in the process this also opened the door to
 all sorts of nasty infelicities that probably breaks the type system,
 control flow, and many other things. Basically, the block inside a
 switch statement essentially amounts to free-for-all spaghetti code
 where you're free to jump around case labels willy-nilly, declare
 variables and jump over their initializations, break out of loops with
 goto case, or enter into the middle of a loop, and all sorts of other
 crazy things that, ostensibly, you shouldn't be able to do in a language
 like D.


yes, `switch` is one of those legacy cans of worms. i'm afraid that it's=20
too late to redesign it, but it would be nice if each `case` will be an=20
implicit `{}` block, and `goto case`/`break` will be allowed only as a=20
last statement in `case` block. and unlabeled code in `switch` should be=20
forbidden to.

but, as i said, it's too late to introduce such breaking change to=20
language.=
Apr 30 2015