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In object-oriented (OO) and functional programming, an immutable object (unchangeable [1] object) is an object whose state cannot be modified after it is created. [2] This is in contrast to a mutable object (changeable object), which can be modified after it is created. [3]
The main difference between an arbitrary data structure and a purely functional one is that the latter is (strongly) immutable. This restriction ensures the data structure possesses the advantages of immutable objects: (full) persistency, quick copy of objects, and thread safety.
Mori.js brings data structures similar to those in Clojure to JavaScript. [32] Immer.js brings an interesting approach where one "creates the next immutable state by mutating the current one". [33] Immer.js uses native JavaScript objects and not efficient persistent data structures and it might cause performance issues when data size is big.
Functional languages also simulate states by passing around immutable states. This can be done by making a function accept the state as one of its parameters, and return a new state together with the result, leaving the old state unchanged. [82] Impure functional languages usually include a more direct method of managing mutable state.
The capturing of final variables enables capturing variables by value. Even if the variable to capture is non-final, it can always be copied to a temporary final variable just before the class. Capturing of variables by reference can be emulated by using a final reference to a mutable container, for example, a one-element array. The local class ...
Arrays, unlike the basic Object type, are prototyped with methods and properties to aid the programmer in routine tasks (for example, join, slice, and push). As in the C family , arrays use a zero-based indexing scheme: A value that is inserted into an empty array by means of the push method occupies the 0th index of the array.
There are multiple ways to implement the flyweight pattern. One example is mutability: whether the objects storing extrinsic flyweight state can change. Immutable objects are easily shared, but require creating new extrinsic objects whenever a change in state occurs. In contrast, mutable objects can share state.
The immutable keyword denotes data that cannot be modified through any reference. The const keyword denotes a non-mutable view of mutable data. Unlike C++ const, D const and immutable are "deep" or transitive, and anything reachable through a const or immutable object is const or immutable respectively. Example of const vs. immutable in D