{{/* (the blank lines at the start are intentional, to separate
     the helper from the function it follows) */}}

func __unmarshal{{.GoName}}(v *{{.GoName}}, m {{ref "encoding/json.RawMessage"}}) error {
    if string(m) == "null" {
        return nil
    }

    var tn struct {
        TypeName string `json:"__typename"`
    }
    err := {{ref "encoding/json.Unmarshal"}}(m, &tn)
    if err != nil {
        return err
    }

    switch tn.TypeName {
    {{range .Implementations -}}
    case "{{.GraphQLName}}":
        {{/* TODO: handle repeated fields! */ -}}
        *v = new({{.GoName}})
        return {{ref "encoding/json.Unmarshal"}}(m, *v)
    {{end -}}
    default:
        return {{ref "fmt.Errorf"}}(
            `Unexpected concrete type for {{.GoName}}: "%v"`, tn.TypeName)
    }
}