Microsoft Certified Solutions Developer (MCSD) Certification Practice Test

In which context can the yield keyword be used?

1. In method declarations

2. In property definitions

3. In iterator methods only

4. In event handlers

The correct answer is: In iterator methods only

The yield keyword is specifically designed to be used within the context of iterator methods, which are methods that return an IEnumerable or IEnumerable<T> collection. When using the yield statement, the method's execution can be paused and resumed, allowing it to produce a sequence of values over time, rather than all at once. When the yield keyword is encountered, the current state of the method is saved, and execution returns the next value in the sequence to the caller. When the caller iterates to the next value, execution resumes from where it was paused. This creates a memory-efficient way to return collections, especially with large data sets, as it generates values on the fly rather than storing them all in memory at once. In contrast, while method declarations, property definitions, and event handlers have their respective purposes, they do not inherently support the function of yielding a value sequentially like iterator methods do. Therefore, the proper context for using the yield keyword is exclusively within iterator methods.