在golang中动态创建结构数组

Question

I try to create a generic function that accepts any struct value and create a array of that struct type. Here is the code I tried. But I get the error "t is not a type". How can I implement this.

    type RegAppDB struct {
    nm   string
    data []interface{}
}

func CreateRegTable(tbl string, rec interface{}) RegAppDB {
    t := reflect.TypeOf(rec)
    fmt.Println(t)
    return RegAppDB{"log", []t}
}

Answer 1

Go does not support generics, and any attempt to do something like that is not going to work out well. In your specific case, there are a couple of key problems:

• You cannot use a variable as a type. Go is compile-time static typed, so anything that gets type information at runtime (ie reflect.TypeOf ) happens too late to use the way you're trying to do it.
• Equally important, your struct's field is of type []interface{} , which means the only type you can use for that field is []interface{} . []string , for example, is a different type, and cannot be assigned to that field.

Answer 2

I took another route. Need some beautification. But this works. So now data is an array of interface and from calling function I pass pointer to structure variables to Save function.

    type RegAppDB struct {
    nm   string
    data []interface{}
    cnt  int
}

// CreateRegTable creates a data structure to hold the regression result
func CreateRegTable(tbl string) *RegAppDB {
    return &RegAppDB{tbl, make([]interface{}, 20), 0}
}

// Save implements saving a record Regression application DB
func (rga *RegAppDB) Save(rec interface{}) error {
    rga.data[rga.cnt] = rec
    rga.cnt++
    return nil
}

// Show implements showing the regression table
func (rga *RegAppDB) Show() error {
    fmt.Println(rga.cnt)
    for i := 0; i <= rga.cnt; i++ {
        fmt.Println(rga.data[i])
    }
    return nil
}

// Compare compares two regression table for equality
func (rga *RegAppDB) Compare(rgt *RegAppDB) bool {
    return reflect.DeepEqual(rga, rgt)
}

Answer 3

It cannot be done for a generic type. If there are a fixed number of possible types, then you can do something like the following:

type RegAppDB struct {
    nm   string
    data interface{}
}

func CreateRegTable(rec interface{}) RegAppDB {
    switch rec.(type) {
    case int:
        return &RegAppDB{"log", []int{}}
    case string:
        return &RegAppDB{"log", []string{}}
    }
    return nil
}

Note: Your data in RegAppDB should be of type interface{} since []int implements interface{} but not []interface{}