immutability

Is it possible to somehow mark a System.Array as immutable. When put behind a public-get/private-set they can't be added to, since it requires re-allocation and re-assignment, but a consumer can still set any subscript they wish: public class Immy { public string[] { get; private set; } } I thought the readonly keyword might do the trick, but no such luck. Ray Jezek ReadOnlyCollection<T> is probably what you are looking for. It doesn't have an Add() method. Quantenmechaniker The Framework Design Guidelines suggest returning a copy of the Array. That way, consumers can't change items from the

In some situations involving immutable objects, it will be possible for many distinct objects to come into existence which are semantically identical. A simple example would be reading many lines of text from a file into strings. From the program's perspective, the fact that two lines have the same sequence of characters would be "coincidence", but from the programmer's perspective a large amount of duplication may be expected. If many string instances are identical, changing the references to those distinct instances into references to a single instance will save memory, and will also

Does the Java standard library have any functional data structures, like immutable Sets, Lists, etc., with functional update? Functional java has Sets, Lists and more interesting abstractions. Have a look at the pcollections project: PCollections serves as a persistent and immutable analogue of the Java Collections Framework. This includes efficient, thread-safe, generic, immutable, and persistent stacks, maps, vectors, sets, and bags, compatible with their Java Collections counterparts. Persistent and immutable datatypes are increasingly appreciated as a simple, design-friendly, concurrency

I've been reading a bit lately about functional languages. Coming from 10+ years of OO development, I'm finding it difficult to get my head around how on earth one can point the pure functional approach (i.e. the same method called with the same parameters does the same thing) at a problem where typically (in an OO program) I would need to cache data. Do we just admit that there might need to be an actor in the program which is not immutable (i.e. the cache). I just watched a presentation by Joe Armstrong on infoq and he seemed pretty dogmatic in this regard! Do we just admit that looking up

I recently learnt about the benefits of EnumMap in Java and would like to replace the existing ImmutableMap<OccupancyType, BigDecimal> to EnumMap. However, I'd also like the immutable property offered by ImmutableMap. Is there a variant, ImmutableEnumMap available in guava ? In terms of storage which one (EnumMap vs ImmutableMap) performs better ? I couldn't find a comparison of the two. I'd appreciate if someone can point me to a link or give some insights on the efficiency of the two data structures ? Louis Wasserman Guava contributor here. Guava doesn't currently have an ImmutableEnumMap

I'm looking for material on persistent data structures that can be used to implement a relational model. Persistence in the meaning of immutable data structures. Anyone know of some good resources, books, papers and such? (I already have the book Purely Functional Data Structures , which is a good example of what I'm looking for.) It is straightforward to modify the ubiquitous B-tree to be persistent. Simply always alloctate a new node whenever a node is modified, and return the new node to the recursive caller, who will insert it at that level by allocating a new node, etc. Ultimate the new

I'm trying to optimise a complex query in PostgreSQL 9.1.2, which calls some functions. These functions are marked STABLE or IMMUTABLE and are called several times with the same arguments in the query. I assumed PostgreSQL would be smart enough to only call them once for each set of inputs - after all, that's the point of STABLE and IMMUTABLE, isn't it? But it appears that the functions are being called multiple times. I wrote a simple function to test this, which confirms it: CREATE OR REPLACE FUNCTION test_multi_calls1(one integer) RETURNS integer AS $BODY$ BEGIN RAISE NOTICE 'Called with %'