the code:
func rlpHash(x interface{}) (h common.Hash) {
hw := sha3.NewKeccak256()
rlp.Encode(hw, x)
hw.Sum(h[:0])
return h
}
If useful:
func (d *state) Sum(in []byte) []byte {
dup := d.clone()
hash := make([]byte, dup.outputLen)
dup.Read(hash)
return append(in, hash...)
}
Full code context see here.
How to understand 'h' here?
Shouldn't assign a value to h first?
'h[:0]' means a zero-value byte?
What a 'h' returned exactly?
'hw.Sum(h[:0])' has a return value ,just ignored?
Confused...
Some thoughts...hope it help:
h[:0] -> create an empty slice from h...but it still refer to the same underlying array.
The slice then is being passed to the method hw.Sum(h[:0]) Note that when you passed a slice to a method, the target method can change value of the slice (because slice is a reference type, search relect.SliceHeader to see why)
If you look at the method Sum. It's actually change the value of the slice h by below line of code:
return append(in, hash...)
So, the return statement do 2 jobs:
in (h in our case)hThey are using named return h, hence for me it's make the code a little bit difficult to read.
By the way, the below code make it clear how the slice work (sorry if not):
package main
import (
"fmt"
)
func Sum(in []byte) []byte {
return append(in, []byte{'a','b'}...)
}
func main() {
h := [4]byte{}
Sum(h[:0])
fmt.Printf("%s
", h) //should print 'ab'
}