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<pre wrap="">Sorry I misunderstood a comment and jumped to a wrong conclusion about: "Currently, Cursor<T> implements Iterable<T> such that you can do...<span
class="moz-txt-citetags"></span>instead, but that's less sensible <u>and will not stay</u>."
Anyway, perhaps there could be a differently-named additional version of next() that returns null (and of fwd()/back() that return booleans), if needed.
Won't "for (;;c.fwd()) {}" loop forever with a Cursor with an OutOfBoundStrategy? :) I don't mean to keep this thread going on and on; I'm sure you'll sort it all out.
Aivar
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On 6/16/10 1:46 PM, Stephan Saalfeld wrote:
<blockquote cite="mid:1276714014.19002.87.camel@tomancak-pc-4"
type="cite">
<pre wrap="">Hi Aivar,
don't take me too literal, that code was just a crazy example :). I
fully agree about not lumping together different kinds of exceptions.
Cursor.getType() (it will BTW be renamed to Cursor.type() because it is
not a getter) may or may not throw an Exception when out of bounds. In
case it does, an appropriate exception is NoSuchElementException that is
thrown by Iterator. Currently, it does not but it should. Keep also in
mind, that this exception is by no means a sign for Cursors being out of
bounds. Cursors with an OutOfBoundsStrategy will very well return a
Type there and not throw such Exception.
I am not deprecating the idea that Cursors are Iterators, why do you
think that? They are Iterators for convenient loop constructs and
scripting language bindings. In addition to Iterators, they can also
move without asking for a value which is sometimes desired.
Best,
Stephan
On Wed, 2010-06-16 at 13:16 -0500, Aivar Grislis wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Cursor<T> c;
try {
for (;;c.fwd()){
// meat of the loop
}
catch (Exception e){}
Using Exceptions for normal program flow might be considered bad Java form, also lumping together IndexOutOfBounds and NoSuchElementException by just catching the general Exception (because it could actually be some other kind of Exception happening).
Cursor.getType() could return null when out of bounds (a possibility Brian mentioned). Cursor.next() would return null also, since you're deprecating the idea of Cursor being an Iterator, it doesn't have to throw that NoSuchElementException.
(You could check for the null to break out of the loop or the code above would still work, at the expense of having two exceptions: e.g. IndexOutOfBounds caught within Cursor and NullPointerException caught here).
Aivar
On 6/16/10 4:29 AM, Stephan Saalfeld wrote:
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<pre wrap=""><a class="moz-txt-link-freetext" href="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">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</a>
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:
</pre>
<blockquote type="cite">
<pre wrap="">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<a class="moz-txt-link-rfc2396E" href="mailto:saalfeld@mpi-cbg.de"><saalfeld@mpi-cbg.de></a> wrote:
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<blockquote type="cite">
<pre wrap="">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:
</pre>
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<pre wrap="">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:
</pre>
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<pre wrap="">Hi,
On Mon, 14 Jun 2010, Stephan Preibisch wrote:
</pre>
<blockquote type="cite">
<pre wrap="">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
}
</pre>
</blockquote>
<pre wrap="">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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