c# no concept of scope ?

jpribele

what scewey logic is c# using for scope? why does the second declaration of lenum cause this code not to compile ? but j is ok ?

using System;
using System.Collections;

public class Test  {

	public static int Main(String[] args) {

	ArrayList b = new ArrayList();
	ArrayList c = new ArrayList();
	for( int i = 0; i < b.Count; i++ ) {
		if( true ) {
			IEnumerator lenum = b.GetEnumerator();
			while( lenum.MoveNext() ) {
				int j = 0;
				j++;
			}
		}
		IEnumerator lenum = c.GetEnumerator();
		while( lenum.MoveNext() ) {
			int j = 0;
			j++;
		}
		
	}
	return 0;
	}

}

Roger Stewart

My guess is that the C# compile knows that the if( true ) block will ALWAYS be executed and optimizes the if statement out. The result is that lenum = b.GetEnumerator() and lenum = c.GetEnumerator() are in the same scope. Roger Stewart "I Owe, I Owe, it's off to work I go..."

jpribele

i just did that as a short example. my actual code where i found that oddity does the same thing.

leppie

This is no different to C. Just brace it.

public class Test
{
public static int Main(String[] args)
{
ArrayList b = new ArrayList();
ArrayList c = new ArrayList();
if( true )
{
IEnumerator lenum = b.GetEnumerator();
while( lenum.MoveNext() )
{
int j = 0;
j++;
}
}
{ //see no problem now
IEnumerator lenum = c.GetEnumerator();
while( lenum.MoveNext() )
{
int j = 0;
j++;
}
}
return 0;
}
}

leppie::AllocCPArticle("Zee blog");

scadaguy

The scopes of the two lenum variables overlap whereas those of the j variables do not. Read section 5.1.7 of the C# language specification. Within the scope of a local variable, it is a compile-time error to refer to the local variable in a textual position that precedes its variable-declarator. However... The lifetime of a local variable is the portion of program execution during which storage is guaranteed to be reserved for it. This lifetime extends from entry into the block, for-statement, switch-statement, or using-statement with which it is associated, until execution of that block, for-statement, switch-statement, or using-statement ends in any way. These two statements together seem to indicate that the compiler is doing what it is suppose to. I wonder why the scope of a variable starts at the entry point of the block and not at the declaration point? Afterall, if you can't reference the variable in a textual position preceding the declaration then why not define its scope in the same manner? I'm sure there's a good answer. I just don't know what it is :) Brian Brian

jpribele

so its not a bug because they say its feature. nice. any other decent language would let this code compile. oh I'll just add it to my list of screwed up things c# does

leppie

So C is not decent. Get a life or go back to whatever decent language you were using previously. PS: did you even read my reply? PSS: using a foreach loop allows you to do that. PSSS: You are infact constructing your IEnumerator loop incorrectly. Here is the proper way:

IEnumerable nodes;
....

for (IEnumerator enumer = nodes.GetEnumerator(); enumer.MoveNext(); )
{
object node = enumer.Current;
...
}

leppie::AllocCPArticle("Zee blog");

Lost User

You could try using a compiler that doesn't punish good programmers for using perfectly legitimate code. Technically, there is no conflict so long as the outer scope lenum comes after the inner scope one. MS's csc and Mono's mcs both use this buggy scoping, however DotGNU Portable.NET's cscc allows this code (as well it should) since there is no conflict. It does reject code where the outer scope variable is declared before the inner scope variable, however (since in that case there is an actual conflict). Rich P.S. For more info on DotGNU check out: http://www.dotgnu.org/

jpribele

leppie wrote: So C is not decent. Get a life or go back to whatever decent language you were using previously. you would think a made i made a comment about your mother. PS: did you even read my reply? i did read your reply but you didn't explain the problem you just posted a work around. PSSS: You are infact constructing your IEnumerator loop incorrectly. Here is the proper way: incorrectly ? there is very little difference between the two and in my opinion the while loop is more readably, you don't have an empty statement as in your for loop. what's the deal anyways. i make a couple of comments about the quirks in the language( every language has them ) and you go off on me like i declare C# as the worst language in the world and every programmer who uses is stupid. now if i have offended anyone, i apologize. but you should remember its just another programming language. i don't think knights running around defending its honour are necessary.

scadaguy

I think you may have misunderstood what the point of the original post was. It was a question about how C# handles scoping. It is a very legitimate and intelligent question. The author was not looking for a work-around. Brian

leppie

jpribele wrote: now if i have offended anyone, i apologize. but you should remember its just another programming language. i don't think knights running around defending its honour are necessary. I think I have misunderstood too. :doh: (rough week/boring weekend) I apologize. From the post below by Rich333 (pnet developer) he clarified it. :) It appears to be a EMCA spec interpretation problem. leppie::AllocCPArticle("Zee blog");
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