Re: [protobuf] modifying lists within a message
Anything with internal in the name may change in future releases, so you
should not rely on it. I will definitely be changing this because it's
supposed to be impossible to obtain a reference to a message that can still
be modified, which calling internalGetResult() would do. Also please assume
that anything marked protected is only intended to be accessed by
subclasses/superclasses, not code that happens to be in the same package, as
this is what I intended when I wrote it. :/
I am open to ideas for how to make this stuff better, but I have certain
requirements that must be met:
1) If code outside the protobuf implementation holds a reference to a
message, it must be guaranteed that that message cannot change after that
point.
2) The interface should not tend to make it more convenient to write
inefficient code than efficient code.
3) The implementation should perform well.
On Wed, Mar 17, 2010 at 1:57 PM, Ron Reynolds tequila...@ymail.com wrote:
but this message isn't built yet - i'm trying to modify a copy of a
previous message wrapping it in a newBuilder so i don't have to copy all the
fields over from the previous (immutable) to the new (mutable until i call
Builder.build()). the only thing (so far) that i can't do to that new
message is remove a single element from its list variable.
you mean it's O(n) because of the shift of all elements after the index
since ArrayList is a continuous block? i wouldn't have called that O(n).
certainly it's O(n) to find the element in the unsorted list, but that's
unavoidable (unless i add code to put the elements in sorted...) once i
find the index of the single element in the list i want i have to remove it
and then add a new (copied and then modified from the original) element to
replace it. (order is unimportant, at least in this case).
and yes, it is true - classes in the same package have access to each
others protected members. package and protected might MEAN something
different but the way the JVM (the Sun JVM anyway) acts the access level is
an int: 0 = public, 1 = protected, 2 = package, 3 = private - you can
access everything = your access-level with respect to the other class.
t'would be a pity for you to fix it - i was rather happy to figure that
one out. :) in which case wiping the entire list and inserting N-1 elements
back in will be my only (non-reflection-based) option (which i'm pretty sure
is more costly than removing a single element from an ArrayList by
index...).
--
*From:* Kenton Varda ken...@google.com
*To:* Ron Reynolds tequila...@ymail.com
*Cc:* protobuf@googlegroups.com
*Sent:* Wed, March 17, 2010 1:32:50 PM
*Subject:* Re: [protobuf] modifying lists within a message
Also note that we cannot return a modifiable list even from the Builder's
getter because the caller could then hold on to that list and modify it
after the message is built. We really need to prevent any kind of
modifications from happening after the message is built.
On Wed, Mar 17, 2010 at 1:31 PM, Kenton Varda ken...@google.com wrote:
On Wed, Mar 17, 2010 at 12:59 PM, Ron Reynolds tequila...@ymail.comwrote:
seems odd that you can delete all via clearXXX() or add via addAllXXX()
and addXXX() but not remove a single element by index...
Our experience is that if we provide a way to remove a single element by
index, people will mistakenly think that the method is more efficient than
clearing the whole list and rebuilding it, when in fact both operations are
O(n). The result of this is that people write loops like:
for (all elements) {
if (shouldFilter(element)) {
remove(element);
}
}
This loop is O(n^2).
well, here's a work-around - if you put a utility class into the same
package as the ProtobufMessages generated class it can access the protected
Builder.internalGetResult() - since package-level access is higher than
protected-level access...
Yikes, is that true? I don't think it is, but if so we need to fix it.
I'm pretty sure protected is neither higher nor lower than package-level
-- it means something entirely different.
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Re: [protobuf] modifying lists within a message
Messages are indeed immutable once built. getXXXList() for both the builder and the message should return unmodifiable lists: if you try to modify them you should get an exception. If you haven't already, take a look at the Java tutorial here: http://code.google.com/apis/protocolbuffers/docs/javatutorial.html For your particular problem I think you'll need do a clearXXX() on the entire list, and add back all the elements except the entry you want to discard. On Wed, Mar 17, 2010 at 7:57 AM, Ron tequila...@ymail.com wrote: i didn't see anything on this in the archives but i admit i didn't do an exhaustive search. i'm using protobuf (2.3.0) to store objects in a Voldemort cluster and am working on the code to modify these objects. so i load the message fine, but it is composed of a list of other messages and i'd like to modify the contents of that list and then stream it back into the cluster. i assumed this is what Type.newBuilder(Type) was for, but have run into an interesting wrinkle trying to modify the list (once i've located the entry i want to remove by index). Builder.getXXXList() returns an unmodifiableList, but the actual message's getXXXList() returns a ref to the actual list (i.e., i could modify the list in the message, but not the list within the message within the builder). i haven't gone through all the code yet but this seemed rather odd since i had thought messages within builders were mutable until build() but once built were considered immutable (tho perhaps that's just in my head). is there a doc showing best practices for modifying Protobuf messages i should be reading? thanks, ...ron. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.comprotobuf%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
Re: [protobuf] modifying lists within a message
When you call Builder.getXXXList(), the underlying list is still modifiable because it's still being built, so it has to convert the list to unmodifiable before returning. But when you call Builder.build(), the underlying list is made unmodifiable. Thus the message's getXXXList() does not need to wrap the list on every call. On Wed, Mar 17, 2010 at 8:57 AM, Ron tequila...@ymail.com wrote: i didn't see anything on this in the archives but i admit i didn't do an exhaustive search. i'm using protobuf (2.3.0) to store objects in a Voldemort cluster and am working on the code to modify these objects. so i load the message fine, but it is composed of a list of other messages and i'd like to modify the contents of that list and then stream it back into the cluster. i assumed this is what Type.newBuilder(Type) was for, but have run into an interesting wrinkle trying to modify the list (once i've located the entry i want to remove by index). Builder.getXXXList() returns an unmodifiableList, but the actual message's getXXXList() returns a ref to the actual list (i.e., i could modify the list in the message, but not the list within the message within the builder). i haven't gone through all the code yet but this seemed rather odd since i had thought messages within builders were mutable until build() but once built were considered immutable (tho perhaps that's just in my head). is there a doc showing best practices for modifying Protobuf messages i should be reading? thanks, ...ron. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.comprotobuf%2bunsubscr...@googlegroups.com . For more options, visit this group at http://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
Re: [protobuf] modifying lists within a message
seems odd that you can delete all via clearXXX() or add via addAllXXX() and addXXX() but not remove a single element by index... well, here's a work-around - if you put a utility class into the same package as the ProtobufMessages generated class it can access the protected Builder.internalGetResult() - since package-level access is higher than protected-level access... From: Jason Hsueh jas...@google.com To: Ron tequila...@ymail.com Cc: Protocol Buffers protobuf@googlegroups.com Sent: Wed, March 17, 2010 9:31:58 AM Subject: Re: [protobuf] modifying lists within a message Messages are indeed immutable once built. getXXXList() for both the builder and the message should return unmodifiable lists: if you try to modify them you should get an exception. If you haven't already, take a look at the Java tutorial here: http://code.google.com/apis/protocolbuffers/docs/javatutorial.html For your particular problem I think you'll need do a clearXXX() on the entire list, and add back all the elements except the entry you want to discard. On Wed, Mar 17, 2010 at 7:57 AM, Ron tequila...@ymail.com wrote: i didn't see anything on this in the archives but i admit i didn't do an exhaustive search. i'm using protobuf (2.3.0) to store objects in a Voldemort cluster and am working on the code to modify these objects. so i load the message fine, but it is composed of a list of other messages and i'd like to modify the contents of that list and then stream it back into the cluster. i assumed this is what Type.newBuilder(Type) was for, but have run into an interesting wrinkle trying to modify the list (once i've located the entry i want to remove by index). Builder.getXXXList() returns an unmodifiableList, but the actual message's getXXXList() returns a ref to the actual list (i.e., i could modify the list in the message, but not the list within the message within the builder). i haven't gone through all the code yet but this seemed rather odd since i had thought messages within builders were mutable until build() but once built were considered immutable (tho perhaps that's just in my head). is there a doc showing best practices for modifying Protobuf messages i should be reading? thanks, ...ron. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups Protocol Buffers group. To post to this group, send email to proto...@googlegroups.com. To unsubscribe from this group, send email to protobuf+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
Re: [protobuf] modifying lists within a message
On Wed, Mar 17, 2010 at 12:59 PM, Ron Reynolds tequila...@ymail.com wrote:
seems odd that you can delete all via clearXXX() or add via addAllXXX() and
addXXX() but not remove a single element by index...
Our experience is that if we provide a way to remove a single element by
index, people will mistakenly think that the method is more efficient than
clearing the whole list and rebuilding it, when in fact both operations are
O(n). The result of this is that people write loops like:
for (all elements) {
if (shouldFilter(element)) {
remove(element);
}
}
This loop is O(n^2).
well, here's a work-around - if you put a utility class into the same
package as the ProtobufMessages generated class it can access the protected
Builder.internalGetResult() - since package-level access is higher than
protected-level access...
Yikes, is that true? I don't think it is, but if so we need to fix it. I'm
pretty sure protected is neither higher nor lower than package-level -- it
means something entirely different.
--
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Re: [protobuf] modifying lists within a message
Also note that we cannot return a modifiable list even from the Builder's
getter because the caller could then hold on to that list and modify it
after the message is built. We really need to prevent any kind of
modifications from happening after the message is built.
On Wed, Mar 17, 2010 at 1:31 PM, Kenton Varda ken...@google.com wrote:
On Wed, Mar 17, 2010 at 12:59 PM, Ron Reynolds tequila...@ymail.comwrote:
seems odd that you can delete all via clearXXX() or add via addAllXXX()
and addXXX() but not remove a single element by index...
Our experience is that if we provide a way to remove a single element by
index, people will mistakenly think that the method is more efficient than
clearing the whole list and rebuilding it, when in fact both operations are
O(n). The result of this is that people write loops like:
for (all elements) {
if (shouldFilter(element)) {
remove(element);
}
}
This loop is O(n^2).
well, here's a work-around - if you put a utility class into the same
package as the ProtobufMessages generated class it can access the protected
Builder.internalGetResult() - since package-level access is higher than
protected-level access...
Yikes, is that true? I don't think it is, but if so we need to fix it.
I'm pretty sure protected is neither higher nor lower than package-level
-- it means something entirely different.
--
You received this message because you are subscribed to the Google Groups
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For more options, visit this group at
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Re: [protobuf] modifying lists within a message
but this message isn't built yet - i'm trying to modify a copy of a previous
message wrapping it in a newBuilder so i don't have to copy all the fields over
from the previous (immutable) to the new (mutable until i call
Builder.build()). the only thing (so far) that i can't do to that new message
is remove a single element from its list variable.
you mean it's O(n) because of the shift of all elements after the index since
ArrayList is a continuous block? i wouldn't have called that O(n). certainly
it's O(n) to find the element in the unsorted list, but that's unavoidable
(unless i add code to put the elements in sorted...) once i find the index of
the single element in the list i want i have to remove it and then add a new
(copied and then modified from the original) element to replace it. (order is
unimportant, at least in this case).
and yes, it is true - classes in the same package have access to each others
protected members. package and protected might MEAN something different
but the way the JVM (the Sun JVM anyway) acts the access level is an int: 0 =
public, 1 = protected, 2 = package, 3 = private - you can access everything =
your access-level with respect to the other class. t'would be a pity for you
to fix it - i was rather happy to figure that one out. :) in which case
wiping the entire list and inserting N-1 elements back in will be my only
(non-reflection-based) option (which i'm pretty sure is more costly than
removing a single element from an ArrayList by index...).
From: Kenton Varda ken...@google.com
To: Ron Reynolds tequila...@ymail.com
Cc: protobuf@googlegroups.com
Sent: Wed, March 17, 2010 1:32:50 PM
Subject: Re: [protobuf] modifying lists within a message
Also note that we cannot return a modifiable list even from the Builder's
getter because the caller could then hold on to that list and modify it after
the message is built. We really need to prevent any kind of modifications from
happening after the message is built.
On Wed, Mar 17, 2010 at 1:31 PM, Kenton Varda ken...@google.com wrote:
On Wed, Mar 17, 2010 at 12:59 PM, Ron Reynolds tequila...@ymail.com wrote:
seems odd that you can delete all via clearXXX() or add via addAllXXX() and
addXXX() but not remove a single element by index...
Our experience is that if we provide a way to remove a single element by
index, people will mistakenly think that the method is more efficient than
clearing the whole list and rebuilding it, when in fact both operations are
O(n). The result of this is that people write loops like:
for (all elements) {
if (shouldFilter(element)) {
remove(element);
}
}
This loop is O(n^2).
well, here's a work-around - if you put a utility class into the same package
as the ProtobufMessages generated class it can access the protected
Builder.internalGetResult() - since package-level access is higher than
protected-level access...
Yikes, is that true? I don't think it is, but if so we need to fix it. I'm
pretty sure protected is neither higher nor lower than package-level -- it
means something entirely different.
--
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