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arg.go
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arg.go
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package util
import (
"errors"
"fmt"
"reflect"
"strings"
)
var (
ErrFlagTagNotFound = errors.New("arg: given field doesn't have a `flag` tag")
ErrStructFieldNotInitialized = errors.New("arg: given field is unitialized")
)
// Uses reflection to retrieve the `flag` tag of a field.
// The value of the `flag` field with the value of the field is
// used to construct a POSIX long flag argument string.
func GetLongFlagFormOfField(fieldValue reflect.Value, fieldType reflect.StructField) (string, error) {
flagTag := fieldType.Tag.Get("flag")
if flagTag == "" {
return "", ErrFlagTagNotFound
}
switch fieldValue.Kind() {
case reflect.Bool:
if fieldValue.Bool() != false {
return fmt.Sprintf("--%v", flagTag), nil
}
return "", ErrStructFieldNotInitialized
case reflect.Int:
if fieldValue.Int() != 0 {
return fmt.Sprintf("--%v=%v", flagTag, fieldValue.Int()), nil
}
return "", ErrStructFieldNotInitialized
case reflect.Array:
fallthrough
case reflect.Slice:
if fieldValue.Len() > 0 {
args := make([]string, 0)
for i := 0; i < fieldValue.Len(); i++ {
args = append(args, fieldValue.Index(i).String())
}
return fmt.Sprintf("--%v=%v", flagTag, strings.Join(args, ",")), nil
}
return "", ErrStructFieldNotInitialized
default:
if fieldValue.String() != "" {
return fmt.Sprintf("--%v=%v", flagTag, fieldValue.String()), nil
}
return "", ErrStructFieldNotInitialized
}
}
// Uses reflection to transform a struct containing fields with `flag` tags
// to a string slice of POSIX compliant long form arguments.
func GetArgumentFormOfStruct(strt interface{}) (flags []string) {
numberOfFields := reflect.ValueOf(strt).NumField()
for i := 0; i < numberOfFields; i++ {
fieldValue := reflect.ValueOf(strt).Field(i)
fieldType := reflect.TypeOf(strt).Field(i)
flagFormOfField, err := GetLongFlagFormOfField(fieldValue, fieldType)
if err != nil {
continue
}
flags = append(flags, flagFormOfField)
}
return
}
func GetFlagFormOfStruct(strt interface{}) (flags []string) {
return GetArgumentFormOfStruct(strt)
}