[ImageJ-devel] [fiji-devel] RE: Simplifying loops?

[Stephan Saalfeld]

http://pacific.mpi-cbg.de/cgi-bin/gitweb.cgi?p=imglib.git;a=blob;f=mpicbg/imglib/cursor/CursorImpl.java;h=6bafb73226e2b0cb90289a382d4d4769c510d62b;hb=master#l81

public T next(){ fwd(); return getType(); }

That is, next() is fwd() + getType(), whereas getType() might be
computationally expensive.  Sometimes, not for each move, you want to
get the value, then next() would slow things down.

Best,
Stephan


On Tue, 2010-06-15 at 08:22 -0500, Brian Selinsky wrote:
> so what is the difference between fwd() and next()?
> 
> if the same I would prefer next() (for consistency) and previous()
> 
> 
> 
> On 06/14/10, Stephan Saalfeld  <saalfeld at mpi-cbg.de> wrote:
> 
> > Self-correction:
> > fwd() and bck() will not return boolean because I do not want them to
> > check anything by default.  In the following example, all pixels are
> > iterated until an exception (e.g. IndexOutOfBounds on type() call)
> > occurs:
> > 
> > Cursor<T> c;
> > try {
> >     for (;;c.fwd()){
> >         // meat of the loop
> > }
> > catch (Exception e){}
> > 
> > I assume that this is the fastest way to iterate over all pixels
> > assuming that something at the basic language level is throwing an
> > appropriate Exception.
> > 
> > Best,
> > Stephan
> > 
> > 
> > 
> > On Mon, 2010-06-14 at 20:06 +0200, Stephan Saalfeld wrote: 
> > > Hi,
> > > 
> > > we implement java.lang.Iterator<T extends Type<T>> where next() returns
> > > T, so no, next() cannot return boolean, fwd() and back() might do that.
> > > In the coming changes, Image<T> implements java.lang.Iterable<T>, such
> > > that the Java language shortcut works:
> > > 
> > > Image< T > image;
> > > for ( final T : image ) {
> > >     // meat of the loop
> > > }
> > > 
> > > How's that?
> > > 
> > > Currently, Cursor<T> implements Iterable<T> such that you can do:
> > > 
> > > Cursor<T> cursor;
> > > for (final T : cursor ) ...
> > > 
> > > instead,  but that's less sensible and will not stay.
> > > 
> > > Best,
> > > Stephan
> > > 
> > > 
> > > 
> > > 
> > > On Mon, 2010-06-14 at 18:54 +0200, Johannes Schindelin wrote: 
> > > > Hi,
> > > > 
> > > > On Mon, 14 Jun 2010, Stephan Preibisch wrote:
> > > > 
> > > > > This is definitely something we could do as far as the linked iterators
> > > > > work. Right now we did not do that because it is quite often extra work,
> > > > > e.g. if you copy an image you need only one check instead of two:
> > > > > 
> > > > > cursor1, cursor2;
> > > > > 
> > > > > while ( cursor1.hasNext() ) 
> > > > > {
> > > > > 	cursor1.fwd();
> > > > > 	cursor2.fwd();
> > > > > 	// meat of the loop
> > > > > }
> > > > 
> > > > Ah, I see. Maybe just a shortcut
> > > > 
> > > > 	public boolean next() {
> > > >         	if (!hasNext())
> > > >                 	return false;
> > > >         	fwd();
> > > >         	return true;
> > > > 	}
> > > > 
> > > > to optimize for the common case?
> > > > 
> > > > Ciao,
> > > > Dscho
> > > > 
> > > 
> > 
> > 
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