Are Go's Type Assertions and Type Switches Slow?

Type Discovery Performance in Go: Are Type Assertions / Type Switches Slow?

In Go, type discovery at runtime can be achieved through type assertions or type switches. While type assertion performs a direct cast, type switch compares against type information. In C/C , runtime type discovery is often considered slow, leading to the use of type member comparisons as a workaround.

Evaluating Performance with Benchmarking

To assess the performance of type discovery mechanisms in Go, we conduct a benchmark test: http://play.golang.org/p/E9H_4K2J9-. The test compares four methods:

• BenchmarkIntmethod: Directly invoking a method on a known type
• BenchmarkInterface: Invoking a method via an interface
• BenchmarkTypeSwitch: Using a type switch to identify and invoke the method
• BenchmarkTypeAssertion: Using a type assertion to identify and invoke the method

Benchmark Results

Edit: October 09, 2019

Recent results with Go v1.12.9 on an AMD R7 2700X demonstrate that the four methods are approximately equal in performance:

BenchmarkIntmethod-16           2000000000           1.67 ns/op
BenchmarkInterface-16           1000000000           2.03 ns/op
BenchmarkTypeSwitch-16          2000000000           1.70 ns/op
BenchmarkTypeAssertion-16       2000000000           1.67 ns/op

Previous Results: January 19, 2015

On an amd64 machine, older results showed that type switch and type assertion were slower than direct method calls or interface method invocations:

BenchmarkIntmethod  1000000000           2.71 ns/op
BenchmarkInterface  1000000000           2.98 ns/op
BenchmarkTypeSwitch 100000000           16.7 ns/op
BenchmarkTypeAssertion  100000000       13.8 ns/op

Conclusion

Based on these results, it can be concluded that type assertions and type switches in Go do not have a significant performance penalty compared to other type checking methodologies. Therefore, selecting the most appropriate approach depends on factors such as code readability and maintenance preferences.

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