包含切片的结构集

Question

I'm trying to implement a toy search algorithm and need to maintain a set of explored states. A state is a struct:

type VWState struct {
    botLocation   VWCoords
    dirtLocations []VWCoords
}

My first thought was that a simple Set could be implemented using a map[VWState]bool , but I can't seem to figure out a way to make it work. If I try to use a VWState as a key to a map, I get the following panic:

Panic: runtime error: hash of unhashable type vw.VWState (PC=0x40EB0D)

Is there a way to make this work? Can I implement a custom hashing function for the struct, or should I be looking at some other ways to implement this?

Any help would be greatly appreciated.

Answer 1

You can use a pointer to your struct as a map key:

map[*VWState]bool

If you want to be able to compare equivalent structs, you can create a method to output a key for the map. String() would be convenient, since you could also use it to print your struct, or tie in a hash function and output something shorter, even an int .

Something as simple as this may suffice, though you could make the output shorter if you like (being careful not to recursively call String() in your format line):

func (s VWState) String() string {
    return fmt.Sprintf("%#v", s)
}

func main() {
    m := make(map[string]bool)
    s := VWState{}
    m[s.String()] = true
}

Answer 2

If there is a sensible maximum length for dirtLocations then you could use an array instead of a slice. Arrays are hashable (provided the element is hashable).

type VWState struct {
    botLocation   VWCoords
    dirtLocations [4]VWCoords
}

You'll then need to either add a count of the number of valid dirtLocations or detect the zero value of VWCoords to work out how many slots in dirtLocations are valid.