Go - Using a map for its set properties with user defined types
- by Seth Hoenig
I'm trying to use the built-in map type as a set for a type of my own (Point, in this case). The problem is, when I assign a Point to the map, and then later create a new, but equal point and use it as a key, the map behaves as though that key is not in the map. Is this not possible to do?
// maptest.go
package main
import "fmt"
func main() {
set := make(map[*Point]bool)
printSet(set)
set[NewPoint(0, 0)] = true
printSet(set)
set[NewPoint(0, 2)] = true
printSet(set)
_, ok := set[NewPoint(3, 3)] // not in map
if !ok {
fmt.Print("correct error code for non existent element\n")
} else {
fmt.Print("incorrect error code for non existent element\n")
}
c, ok := set[NewPoint(0, 2)] // another one just like it already in map
if ok {
fmt.Print("correct error code for existent element\n") // should get this
} else {
fmt.Print("incorrect error code for existent element\n") // get this
}
fmt.Printf("c: %t\n", c)
}
func printSet(stuff map[*Point]bool) {
fmt.Print("Set:\n")
for k, v := range stuff {
fmt.Printf("%s: %t\n", k, v)
}
}
type Point struct {
row int
col int
}
func NewPoint(r, c int) *Point {
return &Point{r, c}
}
func (p *Point) String() string {
return fmt.Sprintf("{%d, %d}", p.row, p.col)
}
func (p *Point) Eq(o *Point) bool {
return p.row == o.row && p.col == o.col
}
