Bug, feature, or misuse? Issue with map container

I'm using Matlab 2012a and I'm trying out map containers and I came across what I think is a bug. I have a variable which is a structure and one of the elements in this structure is a map container. I want to make a copy of the map container and make it a new element in the structure. I then update a value on one of the container values and I find that both containers are updated with the new value.

For example:

X = 10;

Test.Obj1 = containers.Map({'X'},{X});

when I examine the contents, Test.Obj1('X'), I get 10. Now I make a new container and set it equal to the Obj1 container

Obj2 = Test.Obj1;

Now change the value in this new container

Obj2('X') = 20;

Now if I examine Test.Obj1('X') it now equals 20 instead of 10.

Is this a bug or am I misunderstanding containers?

Thanks!

[Jason]

Ok, I just read that because this is a handle class, a copy points back to the original.

I'm not familiar with working with objects in general, so how do I make a copy of a map container that doesn't point back to the original?

[Jason]

Ok, the solution I came up with was to create a function that creates a the container and when call that function to create the "copy".

Not sure if there's a better solution out there so would welcome comments.

Thanks!

[Honglei Chen]

I don't know what's in your function but I have an example below in my answer.

Answer 1

[Honglei Chen]

Here is an example

h1 = containers.Map({'X','Y'},{'X','Y'})
h2 = containers.Map(h1.keys,h1.values)
h2('Z') = 'Z'
h1

HTH

[P Lepage]

It's crazy that there is no official feature to do that, but can manage to find a workaround.

I have data structure made of map<char, map<... etc>>. Since maps stays handles when put in other maps, the solution you provided does not work.

One day I was experimenting with Data Dictionaries (Simulink) and found that the wrapper class Entry returns a deep clone of the object it holds when you call getEntry.

I ended up writing a function that uses this accidental feature to clone my data structure, but it's to slow to be used in a program.

Conclusion : Matlab can break deep references to handle objects, but it wont let you.