How Fast Are Go's Type Assertions and Type Switches, Really?

Type Assertions and Type Switches in Go: Impact on Performance

Type introspection is a common technique for examining the runtime type of an object. However, concerns arise regarding its performance implications. In this article, we explore the speed of type assertions and type switches in Go, comparing them to other type checking methodologies.

Type Discovery Performance

In Go, type assertions and type switches provide a convenient way to identify object types at runtime. While it's known that these mechanisms can incur performance costs in languages like C/C , there's limited clarity on their impact in Go.

Benchmark Evaluation

To assess the performance of type assertions and type switches, we created a benchmark test script (available at http://play.golang.org/p/E9H_4K2J9-). The test compared four methods:

• Int Method: Direct method call on a known type.
• Interface: Method call through an interface.
• Type Switch: Type switch to identify the object type and call the appropriate method.
• Type Assertion: Type assertion to retrieve the underlying type and call the method.

Results and Analysis

The benchmark results indicate that all four methods have comparable speed:

• Updated Results (Oct. 09, 2019):

  • Int Method: 1.67 ns/op
  • Interface: 2.03 ns/op
  • Type Switch: 1.70 ns/op
  • Type Assertion: 1.67 ns/op

• Previous Results (Jan. 19, 2015):

  • Int Method: 2.71 ns/op
  • Interface: 2.98 ns/op
  • Type Switch: 16.7 ns/op
  • Type Assertion: 13.8 ns/op

Conclusion

Contrary to expectations, type assertions and type switches in Go have minimal performance impact compared to other type checking methods. This means that developers can use these techniques without significant concerns about runtime costs. Our benchmark tests demonstrate that all four methods have comparable speed, making them suitable for use in performance-critical applications.

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