invariants

In the book coders at work , the author asks "How do you use invariants in your code". Please explain what this question means. I saw class invariants on wiki , but the example is in Java and I am not skilled enough in Java to relate this example to C#. .NET 4.0 introduces invariance, covariance, and contravariance and is well explained here. Invariance is so broad. The authors usage of the word seems unit test related. For those that read the book, what does the author mean? Are we talking about making an assumption and simply testing the validity after the unit test? The word invariant doesn

I often see the term Invariants in DDD. Here Dino Esposito talks about it. If I look at the .NET library, I see a ValidationAttribute class. Are Invariants and validation rules the same? For example, can I say 50% discount is available only if the order total is more than $250 is an Invariant? Or are they different where Invariants are to protect an object from becoming invalid and validation is to check the validity of the object even after it has changed it's state (it can be in a valid or invalid state)? In the above example, if I use invariants, I check for the invariant before updating

As seen on Introduction to Algorithms ( http://mitpress.mit.edu/algorithms ), the exercise states the following: Input: Array A[1...n] Output: i, where A[i]=v or NIL when not found Write a pseudocode for LINEAR-SEARCH, which scans through the sequence, looking for v. Using a loop invariant, prove that your algorithm is correct. (Make sure that your loop invariant fulfills the three necessary properties – initialization, maintenance, termination.) I have no problem creating the algorithm, but what I don't get is how can I decide what's my loop invariant. I think I understood the concept of loop

I am looking for advice on where to add validation rules for domain entities, and best practices for implementation. I did search and did not find what i was looking for, or i missed it. I would like to know what the recommended way is for validating that properties are not null, in a certain range, or length, etc... I have seen several ways using an IsValid() and other discussions about enforcing in the constructor so the entity is never in an invalid state, or using preprocessing and postprocessing, and others using FluentValidation api, how invariants impact DRY and SRP. Can someone give me

I googled the topic, but besides Wikipedia I didn't find any further useful documentation or articles. Can anybody explain to me in simple words what it means or refer me to some nice and easy to understand documentation? It doesn't mean anything in particular in reference to java. A class invariant is simply a property that holds for all instances of a class, always, no matter what other code does. For example, class X { final Y y = new Y(); } X has the class invariant that there is a y property and it is never null and it has a value of type Y . class Counter { private int x; public int

These are assertions for an algorithm to find the minimum of an array b[h.k]: Precondition: h <= k < b.length Postcondition: b[x] is the minimum of b[h...k] Is this the correct loop for this invariant? invariant: b[x] is the minimum of b[h...t] int x = t; int t = h; // {inv: b[x] is the minimum of b[h...t]} while (t != k) { t = t+1; if (b[t] < b[x]) { x = t;} } You can find the minimum of an array this way (pseudocode): // assume b.length > 0 min = b[0] for i=1 to b.length if b[i] < min min = b[i] To restrict it to b[h, ..., k] : min = b[h] for i=h+1 to k if b[i] < min min = b[i] So you