• Sean Kelly (32/32) Feb 22 2004 First a quick example:
• Sean Kelly (20/20) Feb 22 2004 Just a quick follow-up. A class adaptor is another possibility:
• Ben Hinkle (53/53) Feb 22 2004 "Sean Kelly" wrote in message

Sean Kelly <sean ffwd.cx> writes:

First a quick example:

char[] a = "abc";
int x = 0, y = 1;
foreach( char c; a[x..y] ) {
     printf( "%c", c );
}

will print "a."  This beats the heck out of iterators for most basic 
purposes.  But it leaves me wishing I could operate on reverse ranges 
just as easily.  ie.

foreach( char c; a[y+1..x] ) {
     printf( "%c", c );
}

should print "ba."  This leaves me with one last problem.  I can do:

foreach( char c, a[0..a.length] ) {
     printf( "%c", c );
}

which will print "abc."  But there's no way to refer to the reverse-end 
element.  ie.

foreach( char c, a[a.length..-1] )

I don't like the idea of netagive indexes, but assuming the reverse 
concept goes anywhere there will need to be some way to refer to this 
element for use with foreach.  If this is a bad idea, I suppose we can 
currently fake it:

char[] reverse( char[] src ) {
     char[src.length] dst;
     foreach( int i, char c; src ) {
         dst[src.length-i] = src[i];
     }
     return dst;
}

but it would be nice to avoid the copy if possible.  Comments?


Sean

Sean Kelly <sean ffwd.cx> writes:

Just a quick follow-up.  A class adaptor is another possibility:

class reverse {
public:
     this( char[] src ) {
         m_src = src;
     }
     int opApply( int delegate( inout char ) dg ) {
         for( int i = m_src.length-1; i >= 0; --i ) {
             int r = dg( m_src[i] );
             if( r != 0 ) return r;
         }
         return 0;
     }

private:
     char[] m_src;
};

This might be a bit more difficult for associative ranges, but I think 
still possible.  This being the case, I guess adding a language feature 
really isn't necessary, but I still want it :)


Sean

"Ben Hinkle" <bhinkle4 juno.com> writes:

"Sean Kelly" <sean ffwd.cx> wrote in message
news:c1b6ad$1ejq$1 digitaldaemon.com...
| First a quick example:
|
| char[] a = "abc";
| int x = 0, y = 1;
| foreach( char c; a[x..y] ) {
|      printf( "%c", c );
| }
|
| will print "a."  This beats the heck out of iterators for most basic
| purposes.  But it leaves me wishing I could operate on reverse ranges
| just as easily.  ie.
|
| foreach( char c; a[y+1..x] ) {
|      printf( "%c", c );
| }
|
| should print "ba."  This leaves me with one last problem.  I can do:
|
| foreach( char c, a[0..a.length] ) {
|      printf( "%c", c );
| }
|
| which will print "abc."  But there's no way to refer to the reverse-end
| element.  ie.
|
| foreach( char c, a[a.length..-1] )
|
| I don't like the idea of netagive indexes, but assuming the reverse
| concept goes anywhere there will need to be some way to refer to this
| element for use with foreach.  If this is a bad idea, I suppose we can
| currently fake it:
|
| char[] reverse( char[] src ) {
|      char[src.length] dst;
|      foreach( int i, char c; src ) {
|          dst[src.length-i] = src[i];
|      }
|      return dst;
| }
|
| but it would be nice to avoid the copy if possible.  Comments?
|
|
| Sean
|

A couple of ideas (both cheesy, but what the hey):

1) foreach( char c, a[x..y].dup.reverse) {...}
2) for(uint i = y; i > x;) { char c = a[--i]; ... }

The trouble is 1 still copies and 2 uses "for", which is
slightly more verbose than "foreach".

-Ben