Raúl
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Re:What is that yield return, yield break thing? - 2007/12/22 19:58
When you look for the first time to the C# sample code provided with Robotics Studio you will notice that some new features of this language are extensively used. Statements like yield return, yield break, and IEnumerator<ITask> might call your attention.
Basically, all of this is about Iterators. If you are new to C# 2.0 and want to program robotics applications using Robotics Studio you should clearly understand how Iterators are used.
Iterators can be methods, get accessors or operators that support foreach interation in a class. Usually, if you want to use the foreach statement with a given class you need to implement the IEnumerable interface. However, using Iterators allows you to support foreach iteration in a class without having to implement the entire IEnumerable interface. You just need to write an iterator able to sequentially access the data structures contained in your class. The Visual Studio compiler detects iterators and automatically generates the IEnumerable methods Current, MoveNext and Dispose.
When writting iterators code, the statement yield return is used to return each element in turn, while yield break ends the iteration. The elements returned by yield return <expression> have to be of type IEnumerable or IEnumerator. In the case of Robotics Studio, when we are using the CCR, we usually return a IEnumerator<ITask> (as the generics IEnumerable<T> and IEnumerator<T> can also be used with iterators). Basically, what we are doing is dispatching a collection of tasks.
Have a look to the following links for a detailed explanation and sample code:
C# Programming Guide: Iterators: http://msdn2.microsoft.com/en-us/library/dscyy5s0(VS.80).aspx
yield statement (C# Reference): http://msdn2.microsoft.com/en-us/library/9k7k7cf0(VS.80).aspx
foreach statement (C# reference): http://msdn2.microsoft.com/en-us/library/ttw7t8t6(VS.80).aspx
Using Iterators (C# Programming Guide): http://msdn2.microsoft.com/en-us/library/65zzykke(VS.80).aspx
Raúl Arrabales Moreno. conscious-robots.com/raul |
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