Reducing the cost of object boxing

Language implementations that use a uniform pointer representation for generic datatypes typically apply boxing operations to convert non-uniform objects into the required form. The cost of this boxing process impacts upon the performance of programs that make heavy use of genericity with non-uniform data such as integers and other primitive value types. We show that the overhead of boxing objects into heap storage can be significantly reduced by taking a lazy approach: allowing pointers to stack-allocated objects that are only copied to the heap when necessary. Delaying the boxing of objects avoids unnecessary heap allocation, and results in speedups of around 25% for a range of test programs.