lazy-evaluation

问题 Is there a common term / catch-phrase for the opposite of lazy loading? 回答1: The oposite term for lazy loading is eager loading. Eager loading is essentially computing the tasks when you ask for it. Lazy Loading is when you only do the computation when it is required. 回答2: I've seen the terms "Eager Loading" and "Aggressive Initialization" both used. 回答3: I'd say that the opposite of lazy is proactive loading , i.e. loading something in advance, before it's really needed. However it's hard to

问题 Is there such jQuery plugin? More specific: I want to use some elegant and easy way to postpone some code execution until it's really needed (some event happens). And when this event happens, the postponed code should get executed only once. Some kind of lazy initialization. For example, apply some animation to an element not when document is ready, but when user hovers over that element. I know how to do it the manual way but I don't like it because I have to think about checking and setting

问题 I would like to know what is the python way of initializing a class member but only when accessing it, if accessed. I tried the code below and it is working but is there something simpler than that? class MyClass(object): _MY_DATA = None @staticmethod def _retrieve_my_data(): my_data = ... # costly database call return my_data @classmethod def get_my_data(cls): if cls._MY_DATA is None: cls._MY_DATA = MyClass._retrieve_my_data() return cls._MY_DATA 回答1: You could use a @property on the

问题 I've been learning scala and I gotta say that it's a really cool language. I especially like its pattern matching capabilities and function literals but I come from a javascript, ruby background and one of my favorite patterns in those languages is the lazy function and method definition pattern. An example in javascript is var foo = function() { var t = new Date(); foo = function() { return t; }; return foo(); }; The same code with minor tweaks works in ruby where you just use the singleton

问题 Background This question arises from a challenge Brent Yorgey posed at OPLSS: write a function f :: (Int -> Int) -> Bool that distinguishes f undefined from f (\x -> undefined) . All of our answers either used seq or something like bang patterns that desugar into seq . For example: f :: (Int -> Int) -> Bool f g = g `seq` True *Main> f undefined *** Exception: Prelude.undefined *Main> f (\x -> undefined) True The GHC commentary on seq says that e1 `seq` e2 used to desugar into case e1 of { _ -

问题 Am I right understanding that def is evaluated every time it gets accessed lazy val is evaluated once it gets accessed val is evaluated once it gets into the execution scope? 回答1: Yes, though for the 3rd one I would say "when that statement is executed", because, for example: def foo() { new { val a: Any = sys.error("b is " + b) val b: Any = sys.error("a is " + a) } } This gives "b is null" . b is never evaluated and its error is never thrown. But it is in scope as soon as control enters the

问题 I try to write a simple function wrapping around the dplyr::case_when() function. I read the programming with dplyr documentation on https://cran.r-project.org/web/packages/dplyr/vignettes/programming.html but can't figure out how this works with the case_when() function. I have the following data: data <- tibble( item_name = c("apple", "bmw", "bmw") ) And the following list: cat <- list( item_name == "apple" ~ "fruit", item_name == "bmw" ~ "car" ) Then I would like to write a function like:

问题 I want to calculate powerset of a set. Because I don't need the whole powerset at a time, it's better to generate it lazily. For example: powerset (set ["a"; "b"; "c"]) = seq { set []; set ["a"]; set ["b"]; set ["c"]; set ["a"; "b"]; set ["a"; "c"]; set ["b"; "c"]; set ["a";"b"; "c"]; } Since the result is a sequence, I prefer it in the above order. How can I do it in an idomatic way in F#? EDIT: This is what I'm going to use (based on BLUEPIXY's answer): let powerset s = let rec loop n l =

问题 [ Follows up Check boost::log filter explicitly? ] The following example uses the trivial logger from Boost Log. It outputs 1 , showing that expensive() is only called once. How does it work? Why is expensive() not called? Live On Coliru #include <iostream> #include <boost/log/expressions.hpp> #include <boost/log/trivial.hpp> int count = 0; int expensive() { return ++count; } int main() { boost::log::core::get()->set_filter( boost::log::trivial::severity >= boost::log::trivial::warning );

问题 I implemented a Scott encoded List type in Javascript along with an overloaded append function that mimics the Semigroup typeclass. append works just fine but for large lists it will blow the stack. Here is the decisive part of my implementation: appendAdd("List/List", tx => ty => tx.runList({ Nil: ty, Cons: x => tx_ => Cons(x) (append(tx_) (ty)) })); Usually I use a trampoline to avoid a growing stack, but this presupposes tail recursion and thus won't work in this case. Since this