What is more efficient value or pointer method receivers?
A) Why would you think struct is more efficient?
You are making single call to fetch struct and its fields. Especially given that interce is a struct-wrapper around pointer with type.
B) Why would you think pointer is more efficient?
You are not copying unnecessary data, only pointer is passed to function. Especially given that pointer is always same size.
Result
Overall delta is negligible.
- small structs >>> structs few ns faster
- Subject to codebase, but this is one of common situations. The effect is unnoticeable and dominated by business logic.
- deeply nested large structs >>> pointers is few hundred ns faster
- You have to have very large and nested structs to observe this effect. This is only case when pointer is noticeably faster. Difference can be big. This is effect B)
- deeply nested small structs >>> structs is few ns faster
- You have to have very deep nesting to observe this effect. This is effect A)
$ GOMAXPROCS=1 go test -timeout=1h -bench=. -benchtime=10s -benchmem ./...
goos: darwin
goarch: arm64
pkg: github.com/nikolaydubina/go-bench-receiver
Benchmark_BasicServiceStruct 30910656 373.1 ns/op 0 B/op 0 allocs/op
Benchmark_BasicServicePointer 32115787 374.8 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightStruct_UpStruct 31909561 374.5 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightStruct_UpPointer 32234484 374.6 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightPointer_UpStruct 32067454 374.7 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightPointer_UpPointer 31839183 375.4 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightStruct_UpStructMany_10 30359691 394.3 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightPointer_UpPointerMany_10 30688312 393.1 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightStruct_UpStructMany_50 16043655 748.2 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceLightPointer_UpPointerMany_50 15883161 750.0 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceStruct_UpStruct 31512231 377.9 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceStruct_UpPointer 31865308 377.4 ns/op 0 B/op 0 allocs/op
Benchmark_DepServicePointer_UpStruct 31695372 375.3 ns/op 0 B/op 0 allocs/op
Benchmark_DepServicePointer_UpPointer 32216876 374.4 ns/op 0 B/op 0 allocs/op
Benchmark_DepServiceStruct_UpStructMany_10 23444461 513.5 ns/op 0 B/op 0 allocs/op
Benchmark_DepServicePointer_UpPointerMany_10 30453177 392.7 ns/op 0 B/op 0 allocs/op
Benchmark_EmptyServiceStruct 2979396 4039.0 ns/op 0 B/op 0 allocs/op
Benchmark_EmptyServicePointer 2984328 4034.0 ns/op 0 B/op 0 allocs/op
Why is the result this way?
Looks like sturct/poitner does not matter much to Go runtime. It must be using some lookup table based on type, regardless if it pointer or struct type, for methods of type. Similarly, interface must be resolved to concrete method too. Confirming this with Go source code is area of further research.
