Modern programming languages such as Scala, Java and C# make extensive use of collections. A collection implementation represents a fixed choice in the dimensions of operation time and space utilization. Using the collection in a manner not consistent with this fixed choice can cause significant performance degradation. Often programmers have to choose between under-performing generic collection and specific data-structures at the cost of modularity and ex- tensibility. In his paper, we present and evaluate a generic collection library that automatically choose the appropriate collection implementations for an application. We implemented our solution in the Dotty compiler for Scala and showed that our implementation can choose optimal collections for com- mon basic algorithms.