Slices of structs vs. slices of pointers to structs

Just got curious about this myself. Ran some benchmarks:

type MyStruct struct {
    F1, F2, F3, F4, F5, F6, F7 string
    I1, I2, I3, I4, I5, I6, I7 int64
}

func BenchmarkAppendingStructs(b *testing.B) {
    var s []MyStruct

    for i := 0; i < b.N; i++ {
        s = append(s, MyStruct{})
    }
}

func BenchmarkAppendingPointers(b *testing.B) {
    var s []*MyStruct

    for i := 0; i < b.N; i++ {
        s = append(s, &MyStruct{})
    }
}

Results:

BenchmarkAppendingStructs  1000000        3528 ns/op
BenchmarkAppendingPointers 5000000         246 ns/op

Take aways: we’re in nanoseconds. Probably negligible for small slices. But for millions of ops, it’s the difference between milliseconds and microseconds.

Btw, I tried running the benchmark again with slices which were pre-allocated (with a capacity of 1000000) to eliminate overhead from append() periodically copying the underlying array. Appending structs dropped 1000ns, appending pointers didn’t change at all.