Re: goto skips declaration of variable
On Tuesday, 19 August 2014 at 20:33:00 UTC, monarch_dodra wrote:
On Monday, 18 August 2014 at 13:51:14 UTC, nrgyzer wrote:
Hi all,
I've the following code snipped:
import std.bigint;
void main(string[] args)
{
BigInt i = 12345;
if (args.length 1)
{
goto Exit;
}
i = BigInt(67890);
Exit:
return;
}
For what it's worth, whenever you have goto-end style code,
place all your code in a proper block, in such a way that all
your variable declarations are in that block, and all your
gotos break out of this block. This way, a goto will *never*
cross a declaration, so coding is easy. The only variables you
place at the top or the ones that could need cleanup.
void main(string[] args)
{
//Declarations that need cleanup:
void* p;
//Code
{
BigInt i = 12345; //Local variable
if (args.length 1)
{
goto Exit; //Breaks out of block
}
i = BigInt(67890);
BigInt j = 54321; //Local variable
}
//End
Exit:
CleanUp(p);
return;
}
Yes, that works. I'm using the goto-command to exit my function
if an error (not necessarily an exception) occured. Sure, I can
simply do a return, but I personally prefer a fixed endpoint of
my functions. This also simplifies debugging my application
because I don't need 10 or 20 breakpoints (one before each
return-point).
Re: goto skips declaration of variable
On 08/21/2014 04:12 AM, nrgyzer wrote: I'm using the goto-command to exit my function if an error (not necessarily an exception) occured. Sorry to repeat myself but if an exception occurs in code before the goto, the exit code will not be executed. Of course, it may be that the function is defined 'nothrow' so my concern does not apply. Sure, I can simply do a return, but I personally prefer a fixed endpoint of my functions. Again, that is not possible in a language that has exceptions. Ali
Re: goto skips declaration of variable
On Thursday, 21 August 2014 at 17:39:16 UTC, Ali Çehreli wrote:
On 08/21/2014 04:12 AM, nrgyzer wrote:
I'm using the goto-command to exit my function
if an error (not necessarily an exception) occured.
Sorry to repeat myself but if an exception occurs in code
before the goto, the exit code will not be executed. Of course,
it may be that the function is defined 'nothrow' so my concern
does not apply.
Sure, I can
simply do a return, but I personally prefer a fixed endpoint
of
my functions.
Again, that is not possible in a language that has exceptions.
Ali
Sure, but what about the following pretty simple source:
bool testa(int a)
{
bool fIsValid = (a 0);
if (a 0)
goto Exit;
throw new Exception(int = 0);
Exit:
return fIsValid;
}
int main(string[] args)
{
testa(10); // Use goto
testa(-1); // Throws an exception
}
I'm absolutely aware that gotos are useless if an exception
occured before the goto appears. But in some cases they are very
useful, especially when I want prevent 10 ident-steps or
something else...
Okay, my question was answered - compiler bug. Thanks in advance!
Re: goto skips declaration of variable
On Monday, 18 August 2014 at 17:47:21 UTC, ketmar via Digitalmars-d-learn wrote: On Mon, 18 Aug 2014 13:51:12 + nrgyzer via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: When I try to compile this sample application I'm getting the following error: sample.d(7): Error: goto skips declaration of variable sample.main.__ctmp1344 at sample.d(9) it's compiler bug i believe. but why do you need gotos at the first place? i'm not saying that you must avoid gotos at all costs!, but D has some nice features like scope(exit), scope(success), scope(failure) and nested functions, which can render gotos unnecessary in many cases (and make code cleaner). I know, gotos are having a negative connotation. Sure, I can also use nested functions, but in my opinion it results in dirty and complex code. It's totally overkilled compared to a simple if and goto-instruction. The same regards the scoping... it's simply to much overhead.
Re: goto skips declaration of variable
On Tue, 19 Aug 2014 08:04:54 + nrgyzer via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: goto-instruction. The same regards the scoping... it's simply to much overhead. it's a matter of taste, i think. i myself find 'scope(exit)' excellent, 'cause i'm always keep forgeting to free some resources / restore some state in EXIT: part. ;-) but i'm not saying that everyone should avoid gotos, and this is definitely the bug in compiler that should be fixed. signature.asc Description: PGP signature
Re: goto skips declaration of variable
nrgyzer: Sure, I can also use nested functions, but in my opinion it results in dirty and complex code. It's totally overkilled compared to a simple if and goto-instruction. Often nested functions are less complex, more clean and simpler code compared to using gotos. I suggest to start using nested functions and see how they work out. Bye, bearophile
Re: goto skips declaration of variable
On 08/19/2014 01:04 AM, nrgyzer wrote: On Monday, 18 August 2014 at 17:47:21 UTC, ketmar via but why do you need gotos at the first place? i'm not saying that you must avoid gotos at all costs!, but D has some nice features like scope(exit), scope(success), scope(failure) and nested functions, which can render gotos unnecessary in many cases (and make code cleaner). I know, gotos are having a negative connotation. Sure, I can also use nested functions, but in my opinion it results in dirty and complex code. It's totally overkilled compared to a simple if and goto-instruction. The same regards the scoping... it's simply to much overhead. However, goto is not a substitute for scope(exit) and friends or similar D features because goto may not be executed if an exception is thrown. Ali
Re: goto skips declaration of variable
On Monday, 18 August 2014 at 13:51:14 UTC, nrgyzer wrote:
Hi all,
I've the following code snipped:
import std.bigint;
void main(string[] args)
{
BigInt i = 12345;
if (args.length 1)
{
goto Exit;
}
i = BigInt(67890);
Exit:
return;
}
For what it's worth, whenever you have goto-end style code,
place all your code in a proper block, in such a way that all
your variable declarations are in that block, and all your gotos
break out of this block. This way, a goto will *never* cross a
declaration, so coding is easy. The only variables you place at
the top or the ones that could need cleanup.
void main(string[] args)
{
//Declarations that need cleanup:
void* p;
//Code
{
BigInt i = 12345; //Local variable
if (args.length 1)
{
goto Exit; //Breaks out of block
}
i = BigInt(67890);
BigInt j = 54321; //Local variable
}
//End
Exit:
CleanUp(p);
return;
}
Re: goto skips declaration of variable
nrgyzer:
import std.bigint;
void main(string[] args)
{
BigInt i = 12345;
if (args.length 1)
{
goto Exit;
}
i = BigInt(67890);
Exit:
return;
}
When I try to compile this sample application I'm getting the
following error:
sample.d(7): Error: goto skips declaration of variable
sample.main.__ctmp1344 at sample.d(9)
It looks like a compiler bug (perhaps caused by a rewrite rule).
The 'i' variable is declared before the goto.
Bye,
bearophile
Re: goto skips declaration of variable
It looks like a compiler bug https://issues.dlang.org/show_bug.cgi?id=13321 Bye, bearophile
Re: goto skips declaration of variable
On Mon, 18 Aug 2014 13:51:12 +, nrgyzer wrote: When I try to compile this sample application I'm getting the following error: sample.d(7): Error: goto skips declaration of variable sample.main.__ctmp1344 at sample.d(9) http://dlang.org/changelog.html#disable_goto_skips_init First item in D2.065 Changelog for language changes : 1. Goto jumps now cannot skip variable declarations
Re: goto skips declaration of variable
On 08/18/2014 09:07 AM, ollie wrote: On Mon, 18 Aug 2014 13:51:12 +, nrgyzer wrote: When I try to compile this sample application I'm getting the following error: sample.d(7): Error: goto skips declaration of variable sample.main.__ctmp1344 at sample.d(9) http://dlang.org/changelog.html#disable_goto_skips_init First item in D2.065 Changelog for language changes : 1. Goto jumps now cannot skip variable declarations So, that is the change that caused this regression. nrgyzer's code does not violate that rule. Ali
Re: goto skips declaration of variable
On Mon, 18 Aug 2014 13:51:12 + nrgyzer via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: When I try to compile this sample application I'm getting the following error: sample.d(7): Error: goto skips declaration of variable sample.main.__ctmp1344 at sample.d(9) it's compiler bug i believe. but why do you need gotos at the first place? i'm not saying that you must avoid gotos at all costs!, but D has some nice features like scope(exit), scope(success), scope(failure) and nested functions, which can render gotos unnecessary in many cases (and make code cleaner). signature.asc Description: PGP signature
