New linked list

[Derek Parnell]

On Thu, 11 May 2006 09:52:10 -0700, Walter Bright wrote:

> Sean Kelly wrote:
>> Very cool.  One thing... does this work:
>> 
>>     foreach( Person p; per.each )
>>     {
>>         if( p.age > 50 )
>>             p.listRemove();
>>     }
>> 
>> ie. can you remove elements within a foreach?
> 
> It's undefined behavior. foreach is entitled to assume that the 
> aggregate is a loop invariant, although the contents of the aggregate's 
> elements can change. This precludes things like resizing an array inside 
> a foreach, etc.

This bit my bum yesterday too. I had code inside the foreach that added to
the list, only to discover that even though the elements were added, they
were ignored inside the same foreach loop.

--------- example.d -----------
import std.stdio;
import std.string;
void tester(char[] x)
{
    writefln("Adding '%s'", x);
    vList ~= x;
}

char[][] vList;

void main()
{
    tester("abc");
    tester("def");
    tester("ghi");

version(FOR)
{    for(int i; i < vList.length; i++)
    {
        char[] p = vList[i];
        writefln("Found '%s'", p);
        if (std.string.find(p, "e") != -1)
        {
            tester("orang");
        }
    }

}

version(EACH)
{   foreach(char[] p; vList)
    {
        writefln("Found '%s'", p);
        if (std.string.find(p, "e") != -1)
        {
            tester("orang");
        }
    }

}

}
---------- end of example.d ----------


c:\temp>build example -full -exec -version=FOR
Path and Version : y:\util\build.exe v2.10(1556)
  built on Thu Apr  6 13:13:32 2006
Adding 'abc'
Adding 'def'
Adding 'ghi'
Found 'abc'
Found 'def'
Adding 'orang'
Found 'ghi'
Found 'orang'

c:\temp>build example -full -exec -version=EACH
Path and Version : y:\util\build.exe v2.10(1556)
  built on Thu Apr  6 13:13:32 2006
Adding 'abc'
Adding 'def'
Adding 'ghi'
Found 'abc'
Found 'def'
Adding 'orang'
Found 'ghi'


-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
12/05/2006 10:08:16 AM