clone

I have an array of values that I use as a reference for order when I'm printing out hash values. I'd like to modify the array so that the array values are "prettier". I figured I'd just dup or clone the array, change the values and the original object would remain unchanaged. However (in irb)... @arr = ['stuff', 'things'] a = @arr.clone b = @arr.dup So, at the very least, a and @arr are different objects: a.object_id == @arr.object_id => false But now it gets strange a[0].capitalize! a => ['Stuff', 'things'] @arr => ['Stuff', 'things'] ##<-what? b => ['Stuff', 'things']## <-what??? ok... so

I'm maintaing an older Java code base (jvm 1.4) that seems to use cloning as an alternative to object instantiation, I'm guessing as a performance optimization. Here's a contrived example: public class Foo { private SomeObject obj; // SomeObject implements Cloneable public Foo() { obj = new SomeObject(); obj.setField1("abc"); // these fields will have the same value every time obj.setField2("def"); } public void doStuff() { SomeObject newObj = obj.clone(); // clone it instead of using a factory method // do stuff with newObj } } The usual caveats about premature optimization notwithstanding,

As the definite guide aptly points out (search for "Tags and cloning"): When you run hg clone -r foo to clone a repository as of tag foo , the new clone will not contain any revision newer than the one the tag refers to, including the revision where the tag was created. The result is that you'll get exactly the right subset of the project's history in the new repository, but not the tag you might have expected. It means hg tags in your new clone does NOT show the foo tag. Same thing happens if you had cloned before foo tag was added, and you do hg pull -r foo . (Digression: tag is about the

Algorithm to clone a tree is quite easy, we can do pre-order traversal for that. Is there an efficient algorithm to clone a graph? I tried a similar approach, and concluded we need to maintain a hash-map of nodes already added in the new graph, else there will be duplication of nodes, since one node can have many parents. It suffices to do a depth first search and copy each node as it's visited. As you say, you need some way of mapping nodes in the original graph to corresponding copies so that copies of cycle and cross edges can be connected correctly. This map also suffices to remember nodes

Can someone explain the differences between angular.copy() and JSON.parse(JSON.stringify())? Are there any? What you will recommend to use? Is angular.fromJson(angular.toJson()) the same as JSON.parse(JSON.stringify())? Just to mention, I've read How do I correctly clone a JavaScript object? for JSON.parse(JSON.stringify()) and angular.copy() reference for angular.copy(). What JSON.parse(JSON.stringify()) won't copy: functions any object that has a special representation, like Date (it will get copied but not as Date ) properties with the value undefined angular.fromJson(angular.toJson()) is

I'm using Mongoose and I want to remove the _id property from my Mongoose instance before I send the JSON response to the client. Example: var ui = _.clone(userInvite); delete ui["_id"]; console.log(JSON.stringify(ui)); //still has "_id" property, why? The previous didn't work. However, if I do: var ui = JSON.parse(JSON.stringify(userInvite)); //poor man's clone delete ui["_id"]; console.log(JSON.stringify(ui)); //"_id" is gone! it works! I don't understand why calling delete on a cloned object using Underscore doesn't work, but if I do the hacky JSON.string/JSON.parse, it works. Any thoughts

As discussed before , when a BinaryReader or BinaryWriter gets closed, its underlying Stream get closed as well (aargh). Consider this situation: a routine R is passed a MemoryStream, say M ; I would like to write some stuff to M and then pass it to another routine for more processing (not necessarily writing). For convenience, I'd like to wrap M in a BinaryWriter to do my writing. After writing, I'm done with the BinaryWriter but not with M . void R(MemoryStream M) { using (B = new BinaryWriter(M)) { // write some stuff using B } S(M); // now pass M to another routine for further processing }