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Problem Django querysets are evaluated in a lazy fashion. For example: # models.py: class Author(models.Model): name = models.CharField(max_length=100) class Book(models.Model): author = models.ForeignKey(Author, related_name='books') title = models.CharField(max_length=100) ...

There are places in the standard where an object is copied or moved in order to initialize an object. Copy elision (sometimes called return value optimization) is an optimization whereby, under certain specific circumstances, a compiler is permitted to avoid the copy or move even though the standard...

C++17 Normally, elision is an optimization. While virtually every compiler support copy elision in the simplest of cases, having elision still places a particular burden on users. Namely, the type who's copy/move is being elided must still have the copy/move operation that was elided. For example:...

If you return a prvalue expression from a function, and the prvalue expression has the same type as the function's return type, then the copy from the prvalue temporary can be elided: std::string func() { return std::string("foo"); } Pretty much all compilers will elide the tempor...

When you pass an argument to a function, and the argument is a prvalue expression of the function's parameter type, and this type is not a reference, then the prvalue's construction can be elided. void func(std::string str) { ... } func(std::string("foo")); This says to create a tem...

If you return an lvalue expression from a function, and this lvalue: represents an automatic variable local to that function, which will be destroyed after the return the automatic variable is not a function parameter and the type of the variable is the same type as the function's return type ...

If you use a prvalue expression to copy initialize a variable, and that variable has the same type as the prvalue expression, then the copying can be elided. std::string str = std::string("foo"); Copy initialization effectively transforms this into std::string str("foo"); (th...

Serialization is the process of converting an object into a stream of bytes in order to store the object or transmit it to memory, a database, or a file. Microsoft page Serialization The following example demonstrates Serialization in WCF: [ServiceContract(Namespace="http://Microsoft.Ser...

public class Foo { private const int TASK_ITERATION_DELAY_MS = 1000; private CancellationTokenSource _cts; public Foo() { this._cts = new CancellationTokenSource(); } public void StartExecution() { Task.Factory.StartNew(this.OwnCodeCancelable...

public class Foo { private CancellationTokenSource _cts; public Foo() { this._cts = new CancellationTokenSource(); } public void StartExecution() { Task.Factory.StartNew(this.OwnCodeCancelableTask, this._cts.Token); } public void Cance...

Intervals are simplest way of recording timespans in lubridate. An interval is a span of time that occurs between two specific instants. # create interval by substracting two instants today_start <- ymd_hms("2016-07-22 12-00-00", tz="IST") today_start ## [1] "2016-07-...

Unlike durations, periods can be used to accurately model clock times without knowing when events such as leap seconds, leap days, and DST changes occur. start_2012 <- ymd_hms("2012-01-01 12:00:00") ## [1] "2012-01-01 12:00:00 UTC" # period() considers leap year calculati...

with_tz returns a date-time as it would appear in a different time zone. nyc_time <- now("America/New_York") nyc_time ## [1] "2016-07-22 05:49:08 EDT" # corresponding Europe/Moscow time with_tz(nyc_time, tzone = "Europe/Moscow") ## [1] "2016-07-22 12:49:...

CSS: div{ width:200px; height:200px; background:teal; clip-path: polygon(0 0, 0 100%, 100% 50%); /* refer remarks before usage */ } HTML: <div></div> In the above example, a polygonal clipping path is used to clip the square (200 x 200) element into a triangle shape....

Using Homebrew Prerequisites: Make sure you're on OS X 10.9 (Mavericks) or above, and have Homebrew installed. Run the following in your terminal: brew update && brew install rethinkdb Compile from source Building RethinkDB from source requires OS X 10.9 (Mavericks) or greater. Xcode...

When something fails in your transaction code and you want to undo it, you can rollback your transaction: BEGIN TRY BEGIN TRANSACTION INSERT INTO Users(ID, Name, Age) VALUES(1, 'Bob', 24) DELETE FROM Users WHERE Name = 'Todd' COMMIT TRANSACTION END TRY...

kotlin-gradle-plugin is used to compile Kotlin code with Gradle. Basically, its version should correspond to the Kotlin version you want to use. E.g. if you want to use Kotlin 1.0.3, then you need to aplly kotlin-gradle-plugin version 1.0.3 too. It's a good idea to externalize this version in gradl...

import ( "io/ioutil" "path/filepath" "gopkg.in/yaml.v2" ) func main() { filename, _ := filepath.Abs("config/config.yml") yamlFile, err := ioutil.ReadFile(filename) var config Config err = yaml.Unmarshal(yamlFile, &c...

Extension methods are useful for adding functionality to enumerations. One common use is to implement a conversion method. public enum YesNo { Yes, No, } public static class EnumExtentions { public static bool ToBool(this YesNo yn) { return yn == YesNo.Yes; ...

By default, the navigation pattern works like a stack of pages, calling the newest pages over the previous pages. You will need to use the NavigationPage object for this. Pushing new pages ... public class App : Application { public App() { MainPage = new NavigationPage(new ...