Boxing

This benchmark demonstrates how Go generics speedup scenarios where boxing can be avoided.

• What is boxing?: a summary of boxing
• The example: an exemplar case
• The benchmark: how does it stack up?
• Key takeaways: what it all means

What is boxing?

In general, the term boxing refers to wrapping a value with some container, aka, “putting it inside a box.” For the purposes of this page, the term “boxing” will refer to wrapping some value in Golang with the empty interface, ex.:

x := int(0)
i := interface{}(x)

Generics can be used to eliminate the need for boxing in many situations, which we will highlight with List[T].

The example

This page describes how to run BenchmarkBoxing, a Go-based benchmark that benchmarks lists from the following packages:

• ./lists/boxed: defines type List []interface{}
• ./lists/typed: defines type IntList []int
• ./lists/generic: defines type List[T any] []T

The benchmark

In order to determine the impact of boxing, we will run a Go benchmark that adds random integers to instances of a boxed.List, typed.IntList, and generic.List[int]:

:warning: Please note that Docker may hang if not provided enough resources. The performance improvements are significant enough that the container may be starved for CPU and killed.

docker run -it --rm go-generics-the-hard-way \
  go test -bench Boxing -run Boxing -benchmem -count 5 -v ./06-benchmarks

The following table was generated by piping the above command to hack/b2md.py -t boxing and represents an average across the total number of benchmarks determined by the -count flag:

Key takeaways

A few, key takeaways:

• On average the implementation of List[T any] was more performant than the boxed list:
  • operations were 10x faster
  • consumed half the memory
• The performance improvements were the result of removing the need to box the integer values

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