control-flow | 易学教程

Execution flow in MVC

阅读更多关于 Execution flow in MVC

问题 I am trying to learn MVC in detail, and I am wondering what's the exact functional flow internally, in the sense of which functions (important functions) are called and what they do when the application starts and what functions are called apart from the controller actions that we write in our application as we proceed. 回答1: Here are the detailed steps: Request comes into ASP.NET ASP.NET Routing finds the route match by calling RouteCollection.GetRouteData This in turn calls RouteBase

Implementing ifTrue, ifFalse, ifSome, ifNone, etc. in Scala to avoid if(…) and simple pattern matching

阅读更多关于 Implementing ifTrue, ifFalse, ifSome, ifNone, etc. in Scala to avoid if(…) and simple pattern matching

问题 In Scala, I have progressively lost my Java/C habit of thinking in a control-flow oriented way, and got used to go ahead and get the object I'm interested in first, and then usually apply something like a match or a map() or foreach() for collections. I like it a lot, since it now feels like a more natural and more to-the-point way of structuring my code. Little by little, I've wished I could program the same way for conditions; i.e., obtain a Boolean value first, and then match it to do

How to avoid “if” chains?

阅读更多关于 How to avoid “if” chains?

Assuming I have this pseudo-code: bool conditionA = executeStepA(); if (conditionA){ bool conditionB = executeStepB(); if (conditionB){ bool conditionC = executeStepC(); if (conditionC){ ... } } } executeThisFunctionInAnyCase(); Functions executeStepX should be executed if and only if the previous succeed. In any case, the executeThisFunctionInAnyCase function should be called at the end. I'm a newbie in programming, so sorry for the very basic question: is there a way (in C/C++ for example) to avoid that long if chain producing that sort of "pyramid of code", at the expense of the code

How do I conditionally return different types of futures?

阅读更多关于 How do I conditionally return different types of futures?

I have a method that, depending on a predicate, will return one future or another. In other words, an if-else expression that returns a future: extern crate futures; // 0.1.23 use futures::{future, Future}; fn f() -> impl Future<Item = usize, Error = ()> { if 1 > 0 { future::ok(2).map(|x| x) } else { future::ok(10).and_then(|x| future::ok(x + 2)) } } This doesn't compile: error[E0308]: if and else have incompatible types --> src/lib.rs:6:5 | 6 | / if 1 > 0 { 7 | | future::ok(2).map(|x| x) 8 | | } else { 9 | | future::ok(10).and_then(|x| future::ok(x + 2)) 10 | | } | |_____^ expected struct

How to print the next N executed lines automatically in GDB?

阅读更多关于 How to print the next N executed lines automatically in GDB?

问题 I have been trying to find a way for some time to automate the progress in GDB of tracing the control flow of a program. Even just a simple way of automating the n command so you can see in what order routines are called. I realise that you can issues n x where x is the number of times GDB steps through, but the trouble with that is that it shows the command but not the address of the routine! But if you press n manually in GDB (then press return to issue the previous command) it shows the

How to avoid “if” chains?

阅读更多关于 How to avoid “if” chains?

问题 Assuming I have this pseudo-code: bool conditionA = executeStepA(); if (conditionA){ bool conditionB = executeStepB(); if (conditionB){ bool conditionC = executeStepC(); if (conditionC){ ... } } } executeThisFunctionInAnyCase(); Functions executeStepX should be executed if and only if the previous succeed. In any case, the executeThisFunctionInAnyCase function should be called at the end. I\'m a newbie in programming, so sorry for the very basic question: is there a way (in C/C++ for example)

How do I conditionally return different types of futures?

阅读更多关于 How do I conditionally return different types of futures?

问题 I have a method that, depending on a predicate, will return one future or another. In other words, an if-else expression that returns a future: extern crate futures; // 0.1.23 use futures::{future, Future}; fn f() -> impl Future<Item = usize, Error = ()> { if 1 > 0 { future::ok(2).map(|x| x) } else { future::ok(10).and_then(|x| future::ok(x + 2)) } } This doesn\'t compile: error[E0308]: if and else have incompatible types --> src/lib.rs:6:5 | 6 | / if 1 > 0 { 7 | | future::ok(2).map(|x| x) 8

Swift: guard vs if let

阅读更多关于 Swift: guard vs if let

I have been reading about Optionals in Swift, and I have seen examples where if let is used to check if an Optional holds a value, and in case it does – do something with the unwrapped value. However, I have seen that in Swift 2.0 the keyword guard is used mostly. I wonder whether if let has been removed from Swift 2.0 or if it still possible to be used. Should I change my programs that contain if let to guard ? if let and guard let serve similar, but distinct purposes. The "else" case of guard must exit the current scope. Generally that means it must call return or abort the program. guard is

How to break out of multiple loops?

阅读更多关于 How to break out of multiple loops?

问题 Given the following code (that doesn\'t work): while True: #snip: print out current state while True: ok = get_input(\"Is this ok? (y/n)\") if ok.lower() == \"y\": break 2 #this doesn\'t work :( if ok.lower() == \"n\": break #do more processing with menus and stuff Is there a way to make this work? Or do I have do one check to break out of the input loop, then another, more limited, check in the outside loop to break out all together if the user is satisfied? 回答1: My first instinct would be

Swift: guard vs if let

阅读更多关于 Swift: guard vs if let

问题 I have been reading about Optionals in Swift, and I have seen examples where if let is used to check if an Optional holds a value, and in case it does – do something with the unwrapped value. However, I have seen that in Swift 2.0 the keyword guard is used mostly. I wonder whether if let has been removed from Swift 2.0 or if it still possible to be used. Should I change my programs that contain if let to guard ? 回答1: if let and guard let serve similar, but distinct purposes. The "else" case