lazy-evaluation

There are lots of good questions and answers about foldl , foldr , and foldl' in Haskell. So now I know that: 1) foldl is lazy 2) don't use foldl because it can blow up the stack 3) use foldl' instead because it is strict ( ish ) How foldl is evaluated: 1) a whole bunch of thunks are created 2) after Haskell is done creating thunks, the thunks are reduced 3) overflow the stack if there are too many thunks What I'm confused about: 1) why does reduction have to occur after all thunk-ing? 2) why isn't foldl evaluated just like foldl' ? Is this just an implementation side-effect? 3) from the

Given the Java argument evaluation mechanism , how does Log4j implement lazy evaluation when formatting the message with curly brackets "to avoid the cost of parameter construction" when log is disabled? e.g. logger.debug("Entry number: {} is {}", i, entry[i]); I guess what Log4j means, is that with the curly brackets, they avoid constructing a String when its not necessary (e.g. the Level is not Debug): With logger.debug("Entry number: " + i + " is " + String.valueOf(entry[i])); The String is always calculated even when its not logged. with logger.debug("Entry number: {} is {}", i, entry[i]);

I have a class containing something like the following: public static class Config { private static Lazy<ConfigSource> _cfgSrc = new Lazy<ConfigSource>( () => { /* "ValueFactory" here... */ }, true); public static ConfigSource ConfigSource { get { return _cfgSrc.Value; } } } In accessing the ConfigSource property, I encountered this InvalidOperationException : ValueFactory attempted to access the Value property of this instance. I don't see anything in my "value factory" method that accesses the Value property. Is there anything else that could be triggering this exception? This problem only

I am looking for a way to lazy load my variable, but I want to be able to make it nil later and then recreate it on the get. For example in the instance that there is a memory warning i want to clear anything that isn't used and then recreate it when needed again later. Here is how I would do it in Objective-C and my current interpretation in swift. I am not sure that it preserves the variable for keeping current navigation. Obj-C Implementation @property (strong, nonatomic, readwrite) UINavigationController *navController; ... - (UINavigationController *)navController { if (!_navController) {

Closed . This question is opinion-based. It is not currently accepting answers. Learn more . Want to improve this question? Update the question so it can be answered with facts and citations by editing this post . Closed 11 months ago . I have entity A , which has a many-to-many relation to entity B . So the table layout is : A, AB(mapping table), B To get an object of entity A: I call A.getById() which does getHibernateTemplate().get(A.class, id) using spring and hibernate. The problem is, sometimes ensuing code will just need A, sometimes ensuing code will continue to access the associated B

I often find myself writing a property that is evaluated lazily. Something like: if (backingField == null) backingField = SomeOperation(); return backingField; It is not much code, but it does get repeated a lot if you have a lot of properties. I am thinking about defining a class called LazyProperty: public class LazyProperty<T> { private readonly Func<T> getter; public LazyProperty(Func<T> getter) { this.getter = getter; } private bool loaded = false; private T propertyValue; public T Value { get { if (!loaded) { propertyValue = getter(); loaded = true; } return propertyValue; } } public