Access struct property by name

by

Most code shouldn’t need this sort of dynamic lookup. It’s inefficient compared to direct access (the compiler knows the offset of the X field in a Vertex structure, it can compile v.X to a single machine instruction, whereas a dynamic lookup will need some sort of hash table implementation or similar). It’s also inhibits static typing: the compiler has no way to check that you’re not trying to access unknown fields dynamically, and it can’t know what the resulting type should be.

But… the language provides a reflect module for the rare times you need this.

package main

import "fmt"
import "reflect"

type Vertex struct {
    X int
    Y int
}

func main() {
    v := Vertex{1, 2}
    fmt.Println(getField(&v, "X"))
}

func getField(v *Vertex, field string) int {
    r := reflect.ValueOf(v)
    f := reflect.Indirect(r).FieldByName(field)
    return int(f.Int())
}

There’s no error checking here, so you’ll get a panic if you ask for a field that doesn’t exist, or the field isn’t of type int. Check the documentation for reflect for more details.

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