如何创建自定义哈希码以确定数据是否已突变

Question

Say I have a struct type that has int64 and bools, along with embedded types that have more int64 and bool type fields.

type T1 struct {
   f1 int64
   f2 int64
   f3 bool
   T2 T2
}

type T2 struct {
   f4 int64
   f5 int64
   f6 bool
}

Now using all the structs fields/properties, I want to generate a hashcode.

The aim of this is so I can determine if the contents of the instance has changed but comparing the before/after hashcode value.

So if T1 instance has changed i.e. any of its own properties Then the value of the hash should be different.

Answer 1

You can use something like:

func (t *T1) Hash() uint64 {
    hb := make([]byte, 8+8+1+8+8+1)
    binary.BigEndian.PutUint64(hb, uint64(t.f1))
    binary.BigEndian.PutUint64(hb[8:], uint64(t.f2))
    if t.f3 {
        hb[16] = 1
    }
    binary.BigEndian.PutUint64(hb[17:], uint64(t.T2.f4))
    binary.BigEndian.PutUint64(hb[25:], uint64(t.T2.f5))
    if t.T2.f6 {
        hb[33] = 1
    }
    f := fnv.New64a()
    f.Write(hb)
    return f.Sum64()
}

<kbd>playground</kbd>

Although if you are using it as a map key, it's better to just directly use the struct as the key and let go handle it.