mutable

This question is about the Data.Vector package. Given the fact that I'll never use the old value of a certain cell once the cell is updated. Will the update operation always create a new vector, reflecting the update, or will it be done as an in-place update ? Note: I know about Data.Vector.Mutable No, but something even better can happen. Data.Vector is built using "stream fusion" . This means that if the sequence of operations that you are performing to build up and then tear down the vector can be fused away, then the Vector itself will never even be constructed and your code will turn into

I wonder if String arrays in Java are mutable ? I know that Strings are immutable, but how about string Arrays ? If I have a string array, and change the content, will a new string object be created ? Or will the actual value just be changed ? Thanks in advance Luiggi Mendoza The String s contained in the String[] are indeed immutable, but the array is mutable. This is well explained in this answer : Immutability means that objects of a certain type can not change in any meaningful way to outside observers Integer , String , etc are immutable Generally all value types should be Array objects

I've got a relatively expensive data-fetching operation that I want to cache the results of. This operation is called from const methods, roughly like this: double AdjustData(double d, int key) const { double factor = LongRunningOperationToFetchFactor(key); return factor * d; } I'd like AdjustData to remain const , but I want to cache out the factor so I only fetch it the first time. At present I'm using a mutable map<int, double> to store the result (the map being from key to factor ), but I'm thinking using a function-scoped static might be a better solution - this factor is only needed by

Initial note: I'm working in Julia, but this question probably applies to many languages. Setup: I have a composite type as follows: type MyType x::Vector{String} end I write some methods to act on MyType . For example, I write a method that allows me to insert a new element in x , e.g. function insert!(d::MyType, itemToInsert::String) . Question: Should MyType be mutable or immutable? My understanding: I've read the Julia docs on this, as well as more general (and highly upvoted) questions on Stackoverflow (e.g. here or here ), but I still don't really have a good handle on what it means to