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;
}

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)

I know that the error is caused by the line 'i = BigInt("67890")'. I also know that I can simply replace the goto-condition with something like this:

if (args.length == 0)
{
	i = BigInt("67890");
}

But that's not what I want because I've many BigInt-assignments in my real application. That would result in a very very deep, nested source structure and that really hurts. So, is there any solution how I can realize the BigInt-assignment after the goto-Command (or better: without skipping the declaration)?

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

> It looks like a compiler bug

https://issues.dlang.org/show_bug.cgi?id=13321

Bye,
bearophile

On Mon, 18 Aug 2014 13:51:12 +0000, 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

On 08/18/2014 09:07 AM, ollie wrote:
> On Mon, 18 Aug 2014 13:51:12 +0000, 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

On Mon, 18 Aug 2014 13:51:12 +0000
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).

On Monday, 18 August 2014 at 17:47:21 UTC, ketmar via Digitalmars-d-learn wrote:
> On Mon, 18 Aug 2014 13:51:12 +0000
> 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.

On Tue, 19 Aug 2014 08:04:54 +0000
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.

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

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