On Sun, May 3, 2015 at 5:42 AM, Thomas Passin <list1@t...> wrote:

>

> Well, actually, there is nothing to indicate that these two objects are the same.  

> A _javascript_ engine would create two objects, and if you were to change

> the properties of one, the other's properties would not automatically change.

 

Agreed. The example, and the way I am using this is strongly based on assumption that the objects are immutable.

We also need to remember, that JSON is widely used not only for representing _javascript_ objects, but also in other important cases -- for example to express the input data for REST web services (seen in practice with the most widely used HTTP verbs)  and for their response.

JSON is just a specific serialization mechanism -- how JSON would be de-serialized depends solely on the receiving end -- it may be serialized to something completely different than a _javascript_ object.

Any good particular implementation would use objects immutability for sharing and efficiency.

 

For the XPath 3.1 map datatype, this is what makes possible to have efficient (sub-linear) implementations of   map:put() and    map:remove().

 

Even in a language such as C# there are some immutable objects, such as the string object. This led to a powerful string sharing feature: interned strings: https://msdn.microsoft.com/en-us/library/system.string.intern(v=vs.110).aspx

 

 

--

Cheers,

Dimitre Novatchev