C# linq yield return

Wenn eine yield return-Anweisung im Iterator erreicht wir wird ein expression-Ausdruck zurückgegeben, und die aktuelle Position im Code wird beibehalten. The following example shows the two forms of the yield statement. You use a yield return statement to return each element one at a time. When a yield return statement is reached in the iterator metho expression is returne and the current location in code is retained. The sequence returned from an iterator method can be consumed by using a foreach statement or LINQ query.

In this post I want to explain what it does and what its applications are. Even if most developers have heard of yield return it’s often misunderstood. Active year, months ago. Wenn eine yield return -Anweisung im Iterator erreicht wir wird ein expression-Ausdruck zurückgegeben, und die aktuelle Position im Code wird beibehalten. GetThePrimaryIds() , then call GetTheOtherIds() , then call Concat().

When you use the yield contextual keyword in a statement, you indicate that the metho operator, or get accessor in which it appears is an iterator. Rewrite this foreach yield to a linq yield? Yield return is similar to a return statement (which passes control flow to the calling method), followed by a goto to the yield statement in the next iteration of the foreach.

And if your enumeration had been something stateful, like reading bytes from a stream, or a random number generator, the second evaluation would not give the same as the first. Tip: This behavior does not exist in the Common Language Runtime. It’s not just yield return that does this — anything out of a LINQ expression is similarly lazily evaluated. Quote from MSDN The yield keyword signals to the compiler that the method in which it appears is an iterator block.

Here is a quick example. Can somebody show me a pra. Don’t use ref or out keyword with the parameters of metho operator or property. The declaration of yield must meet the following requirements. Linq の話はあまりでてきません。ご容赦ください。 リファクタリング手順.

But sometimes, you want to end the method prematurely. The return part of yield - return is potentially misleading to those not familiar with the yield - return statement, because return by itself unconditionally transfers control out of a method. Important point about yield return is that, every time the flow of control is passed to the caller, she has an additional opportunity to look at the item and make some business decision about it without having to wait for the entire filtered list to come back to her. And there is no temp table, no yield return being used here.

Bei Erreichen von yield return wird die aktuelle Position gespeichert, und beim nächsten Aufruf der Schleife wird die Ausführung von dieser Position neu gestartet. I think LINQ is where yield - return becomes most useful since it provides mechanism for deferred loading. Mehr haben Sie nicht zu tun, denn im Hintergrund generiert der Compiler automatisch die Methoden Current und MoveNext der IEnumerator-Schnittstelle, wenn er yield erkennt.

Somit gewährleistet es Typsicherheit bereits zur Übersetzungszeit. Sogenannte LINQ -Anbieter (englisch LINQ provider) übersetzen die LINQ -Anweisungen in die speziellen Zugriffsmethoden der jeweiligen Datenquelle. NET präsentiert LINQ die Abfrage-Ergebnisse als streng typisierte Aufzählungen. In a normal (non-iterating) method you would use the return keyword. In other words, yield break for an iterator is the same as return for a standard method.

DEMO之后用ILSpy看源码，就知道了） 编辑器遇到上面的情况会将生成一些类来保存 yield return 的所有调用都一一做分支处理（状态机分支），下次对IEnumerator. При обращении к оператору yield return будет сохраняться текущее местоположение. For example, LINQ -to-objects is built on yield return. Aber manchmal möchten Sie die Methode vorzeitig beenden.

In einer normalen (nicht iterierenden) Methode würden Sie das Schlüsselwort return. Aber man kann nicht verwenden return in einem Iterator, haben Sie verwenden yield break. Have you tried doing a yield return inside an async method? IEnumerable 介面的物件集合時, 是使用 yield return 來取代原來的 return 指令。 Code： using System. Iterator メソッドを呼び出します。 yield return ステートメントが Iterator メソッドに到達すると、expression が返され、コードの現在の位置が保持されます。 次回、Iterator 関数が呼び出されると、この位置から実行が再開され.

In fact, it won’t even compile. This quickly died down, as far as I can see anyway. Either people forgot the idea, or it became such boringly standard practice that no one ever. Słowo kluczowe yield pozwala na przygotowanie niestandardowych iteracji dokonywanych na kolekcjach. Możemy wyróżnić dwa scenariusze w których.

Skip Navigation Links Home: Jump statements: yield. This keyword is placed before return. It is only used on enumerators. We use it in the previous example method that returns IEnumerable.

State: We can use yield to save the state of the function after the return. This work is performed by the compiler.