closures

问题 I was playing around with Rust closures when I hit this interesting scenario: fn main() { let mut y = 10; let f = || &mut y; f(); } This gives an error: error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements --> src/main.rs:4:16 | 4 | let f = || &mut y; | ^^^^^^ | note: first, the lifetime cannot outlive the lifetime as defined on the body at 4:13... --> src/main.rs:4:13 | 4 | let f = || &mut y; | ^^^^^^^^^ note: ...so that closure can access

问题 I was playing around with Rust closures when I hit this interesting scenario: fn main() { let mut y = 10; let f = || &mut y; f(); } This gives an error: error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements --> src/main.rs:4:16 | 4 | let f = || &mut y; | ^^^^^^ | note: first, the lifetime cannot outlive the lifetime as defined on the body at 4:13... --> src/main.rs:4:13 | 4 | let f = || &mut y; | ^^^^^^^^^ note: ...so that closure can access

问题 I was reading the comments on an answer and saw this comment: [the closure] doesn't persist the state of foo so much as creates a special scope containing (1) the returned function and (2) all the external variables referenced at the time of the return. This special scope is called a closure. OK, so far so good. Now here is the interesting part that I didn't know about: Case in point... if you had another var defined in foo that was not referenced in the return function, it would not exist in

问题 I understand that closures keep the execution context alive by saving a reference to the executed function. I'm wondering whether the whole context is saved or only the required parts. In the former case I need to structure the functions in a way that no memory is wasted. This should be the design goal anyway, but I would like to know if JavaScript takes care of it, too. Here's a simple example (on the basis of Single Page Web Applications , Mikowski/Powell, p. 56): var ctx; var outer

问题 So if a language provides higher order procedure then I can have procedure that returns procedure. Something like: (define (Proc a b c) (lambda (x) ( #| method body here in terms of a b c and x |# ))) To create new procedure, I would just do something like: (define ProcA (Proc a1 b1 c1)) ; Would create ProcA that has 1 argument Similar task could be done in a language which does not support higher order procedure by defining Proc that takes 4 instead of 3 arguments and calling this procedure

问题 So if a language provides higher order procedure then I can have procedure that returns procedure. Something like: (define (Proc a b c) (lambda (x) ( #| method body here in terms of a b c and x |# ))) To create new procedure, I would just do something like: (define ProcA (Proc a1 b1 c1)) ; Would create ProcA that has 1 argument Similar task could be done in a language which does not support higher order procedure by defining Proc that takes 4 instead of 3 arguments and calling this procedure

问题 This is a follow up question from :: (double colon) operator in Java 8 in which Java allows you to refer to methods using :: operator. Is it possible to provide some custom Functional Interface that I create and use it with :: operator? And how to do it? 回答1: “Is it possible to provide some custom Functional Interface that I create and use it with :: operator? And how to do it?” It is possible and it’s as easy as you could imagine: just create an interface with exactly one method. You don’t

问题 I saw this Javascript quiz here: http://www.netfxharmonics.com/2008/01/NetFX-Harmonics-JavaScript-Quiz and I could not figure out this problem: (function(){ var a = 1; var b = 2; (function( ) { a = b; var b; })( ); console.log('a:'+ a); // => "a:undefined" console.log('b:'+ b); // => "b:2" })() However, if you remove the var b; declaration from the inner function, then a == 2 as you would expect. Why is this happening? (You can play with it here: http://jsfiddle.net/gnhMZ/) 回答1: It's

问题 typealias IntMaker = (Void)->Int func makeCounter() ->IntMaker{ var n = 0 // Line A func adder()->Integer{ n = n + 1 return n } return adder } let counter1 = makeCounter() counter1() // returns 1 counter1() // returns 2 counter1() // returns 3 Isn't 'Line A' called each time we call counter1() ? meaning that var n = 0 should be called every time... Why is that the counter returns different values? Shouldn't they always be returning '1' ? 回答1: You've called makeCounter() once. That creates

问题 I come from the Java world, where you can hide variables and functions and then run unit tests against them using reflection. I have used nested functions to hide implementation details of my classes so that only the public API is visible. I am trying to write unit tests against these nested functions to make sure that I don't break them as I develop. I have tried calling one of the nested functions like: def outer(): def inner(): pass outer.inner() which results in the error message: