basic first version working
This commit is contained in:
commit
408290f7c2
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@ -0,0 +1,268 @@
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package arguments
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import (
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"fmt"
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"os"
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"reflect"
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"strconv"
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"strings"
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)
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// MustParse processes command line arguments and exits upon failure.
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func MustParse(dest interface{}) {
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err := Parse(dest)
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if err != nil {
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fmt.Println(err)
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os.Exit(1)
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}
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}
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// Parse processes command line arguments and stores the result in args.
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func Parse(dest interface{}) error {
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return ParseFrom(dest, os.Args)
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}
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// ParseFrom processes command line arguments and stores the result in args.
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func ParseFrom(dest interface{}, args []string) error {
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v := reflect.ValueOf(dest)
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if v.Kind() != reflect.Ptr {
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panic(fmt.Sprintf("%s is not a pointer type", v.Type().Name()))
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}
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v = v.Elem()
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// Parse the spec
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spec, err := extractSpec(v.Type())
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if err != nil {
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return err
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}
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// Process args
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err = processArgs(v, spec, args)
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if err != nil {
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return err
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}
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// Validate
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return validate(spec)
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}
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// spec represents information about an argument extracted from struct tags
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type spec struct {
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field reflect.StructField
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index int
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long string
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short string
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multiple bool
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required bool
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positional bool
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help string
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wasPresent bool
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}
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// extractSpec gets specifications for each argument from the tags in a struct
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func extractSpec(t reflect.Type) ([]*spec, error) {
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if t.Kind() != reflect.Struct {
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panic(fmt.Sprintf("%s is not a struct pointer", t.Name()))
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}
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var specs []*spec
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for i := 0; i < t.NumField(); i++ {
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// Check for the ignore switch in the tag
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field := t.Field(i)
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tag := field.Tag.Get("arg")
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if tag == "-" {
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continue
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}
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spec := spec{
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long: strings.ToLower(field.Name),
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field: field,
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index: i,
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}
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// Get the scalar type for this field
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scalarType := field.Type
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if scalarType.Kind() == reflect.Slice {
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spec.multiple = true
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scalarType = scalarType.Elem()
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if scalarType.Kind() == reflect.Ptr {
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scalarType = scalarType.Elem()
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}
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}
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// Check for unsupported types
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switch scalarType.Kind() {
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case reflect.Array, reflect.Chan, reflect.Func, reflect.Interface,
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reflect.Map, reflect.Ptr, reflect.Struct,
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reflect.Complex64, reflect.Complex128:
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return nil, fmt.Errorf("%s.%s: %s fields are not supported", t.Name(), field.Name, scalarType.Kind())
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}
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// Look at the tag
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if tag != "" {
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for _, key := range strings.Split(tag, ",") {
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var value string
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if pos := strings.Index(key, ":"); pos != -1 {
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value = key[pos+1:]
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key = key[:pos]
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}
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switch {
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case strings.HasPrefix(key, "--"):
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spec.long = key[2:]
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case strings.HasPrefix(key, "-"):
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if len(key) != 2 {
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return nil, fmt.Errorf("%s.%s: short arguments must be one character only", t.Name(), field.Name)
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}
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spec.short = key[1:]
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case key == "required":
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spec.required = true
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case key == "positional":
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spec.positional = true
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case key == "help":
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spec.help = value
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default:
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return nil, fmt.Errorf("unrecognized tag '%s' on field %s", key, tag)
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}
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}
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}
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specs = append(specs, &spec)
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}
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return specs, nil
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}
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// processArgs processes arguments using a pre-constructed spec
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func processArgs(dest reflect.Value, specs []*spec, args []string) error {
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// construct a map from arg name to spec
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specByName := make(map[string]*spec)
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for _, spec := range specs {
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if spec.long != "" {
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specByName[spec.long] = spec
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}
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if spec.short != "" {
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specByName[spec.short] = spec
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}
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}
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// process each string from the command line
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var allpositional bool
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var positionals []string
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// must use explicit for loop, not range, because we manipulate i inside the loop
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for i := 0; i < len(args); i++ {
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arg := args[i]
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if arg == "--" {
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allpositional = true
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continue
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}
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if !strings.HasPrefix(arg, "-") || allpositional {
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positionals = append(positionals, arg)
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continue
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}
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// check for an equals sign, as in "--foo=bar"
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var value string
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opt := strings.TrimLeft(arg, "-")
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if pos := strings.Index(opt, "="); pos != -1 {
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value = opt[pos+1:]
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opt = opt[:pos]
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}
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// lookup the spec for this option
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spec, ok := specByName[opt]
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if !ok {
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return fmt.Errorf("unknown argument %s", arg)
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}
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spec.wasPresent = true
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// deal with the case of multiple values
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if spec.multiple {
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var values []string
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if value == "" {
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for i++; i < len(args) && !strings.HasPrefix(args[i], "-"); i++ {
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values = append(values, args[i])
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}
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} else {
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values = append(values, value)
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}
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setSlice(dest, spec, values)
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continue
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}
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// if it's a flag and it has no value then set the value to true
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if spec.field.Type.Kind() == reflect.Bool && value == "" {
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value = "true"
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}
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// if we have something like "--foo" then the value is the next argument
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if value == "" {
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if i+1 == len(args) || strings.HasPrefix(args[i+1], "-") {
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return fmt.Errorf("missing value for %s", arg)
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}
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value = args[i+1]
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i++
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}
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err := setScalar(dest.Field(spec.index), value)
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if err != nil {
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return fmt.Errorf("error processing %s: %v", arg, err)
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}
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}
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return nil
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}
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// validate an argument spec after arguments have been parse
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func validate(spec []*spec) error {
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for _, arg := range spec {
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if arg.required && !arg.wasPresent {
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return fmt.Errorf("--%s is required", strings.ToLower(arg.field.Name))
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}
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}
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return nil
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}
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// parse a value as the apropriate type and store it in the struct
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func setSlice(dest reflect.Value, spec *spec, values []string) error {
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// TODO
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return nil
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}
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// set a value from a string
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func setScalar(v reflect.Value, s string) error {
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if !v.CanSet() {
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return fmt.Errorf("field is not writable")
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}
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switch v.Kind() {
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case reflect.String:
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v.Set(reflect.ValueOf(s))
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case reflect.Bool:
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x, err := strconv.ParseBool(s)
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if err != nil {
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return err
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}
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v.Set(reflect.ValueOf(x))
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
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x, err := strconv.ParseInt(s, 10, v.Type().Bits())
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if err != nil {
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return err
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}
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v.Set(reflect.ValueOf(x).Convert(v.Type()))
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case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
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x, err := strconv.ParseUint(s, 10, v.Type().Bits())
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if err != nil {
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return err
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}
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v.Set(reflect.ValueOf(x).Convert(v.Type()))
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case reflect.Float32, reflect.Float64:
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x, err := strconv.ParseFloat(s, v.Type().Bits())
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if err != nil {
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return err
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}
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v.Set(reflect.ValueOf(x).Convert(v.Type()))
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default:
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return fmt.Errorf("not a scalar type: %s", v.Kind())
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}
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return nil
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}
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@ -0,0 +1,88 @@
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package arguments
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import (
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"strings"
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"testing"
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"github.com/stretchr/testify/assert"
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"github.com/stretchr/testify/require"
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)
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func split(s string) []string {
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return strings.Split(s, " ")
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}
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func TestStringSingle(t *testing.T) {
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var args struct {
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Foo string
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}
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err := ParseFrom(&args, split("--foo bar"))
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require.NoError(t, err)
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assert.Equal(t, "bar", args.Foo)
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}
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func TestMixed(t *testing.T) {
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var args struct {
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Foo string `arg:"-f"`
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Bar int
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Ham bool
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Spam float32
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}
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args.Bar = 3
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err := ParseFrom(&args, split("-spam=1.2 -ham -f xyz"))
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require.NoError(t, err)
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assert.Equal(t, "xyz", args.Foo)
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assert.Equal(t, 3, args.Bar)
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assert.Equal(t, true, args.Ham)
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assert.Equal(t, 1.2, args.Spam)
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}
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func TestRequired(t *testing.T) {
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var args struct {
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Foo string `arg:"required"`
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}
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err := ParseFrom(&args, nil)
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require.Error(t, err, "--foo is required")
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}
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func TestShortFlag(t *testing.T) {
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var args struct {
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Foo string `arg:"-f"`
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}
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err := ParseFrom(&args, split("-f xyz"))
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require.NoError(t, err)
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assert.Equal(t, "xyz", args.Foo)
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err = ParseFrom(&args, split("-foo xyz"))
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require.NoError(t, err)
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assert.Equal(t, "xyz", args.Foo)
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err = ParseFrom(&args, split("--foo xyz"))
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require.NoError(t, err)
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assert.Equal(t, "xyz", args.Foo)
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}
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func TestCaseSensitive(t *testing.T) {
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var args struct {
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Lower bool `arg:"-v"`
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Upper bool `arg:"-V"`
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}
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err := ParseFrom(&args, split("-v"))
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require.NoError(t, err)
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assert.True(t, args.Lower)
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assert.False(t, args.Upper)
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}
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func TestCaseSensitive2(t *testing.T) {
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var args struct {
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Lower bool `arg:"-v"`
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Upper bool `arg:"-V"`
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}
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err := ParseFrom(&args, split("-V"))
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require.NoError(t, err)
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assert.False(t, args.Lower)
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assert.True(t, args.Upper)
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}
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