This sample code uses array expansion with dot notation and has performance issues: What best...

In the Guidewire InsuranceSuite Developer training, specifically within the Advanced Gosu modules, the " Array Expansion Operator " (*.) is identified as a double-edged sword. While it provides a clean, declarative syntax for gathering properties from an array of objects into a new collection, it is a common source of performance degradation in complex configurations.

The technical reason for this performance hit is that every time the expansion operator is invoked, Gosu must create an intermediate, temporary collection in memory to hold the projected values. If you are expanding multiple levels (e.g., Claim.Exposures*.Contacts*.Address), the system is essentially building multiple " throwaway " lists in the application server ' s heap. For large datasets, this leads to high memory overhead and triggers frequent garbage collection cycles, which slows down the entire application.

Guidewire’s official recommendation is to rewrite the code using a nested for loop (Option A). By using explicit procedural iteration, the developer eliminates the need for these hidden intermediate collections. A nested loop allows for " streaming " the data—processing each item as it is reached rather than collecting everything into a list first. This is significantly more memory-efficient. Additionally, nested loops allow developers to integrate " early exit " logic or filters that can prevent the system from even attempting to load certain records from the database, further optimizing the transaction. Following this best practice ensures that the code is not only easier to debug using the Guidewire Profiler but also scales predictably as the insurer ' s data volume grows.