add support for IP address, email address, and MAC address

parse.go

@@ -1,7 +1,6 @@
 package arg
 
 import (
-	"encoding"
 	"errors"
 	"fmt"
 	"os"
@@ -20,16 +19,13 @@ type spec struct {
 	help       string
 	env        string
 	wasPresent bool
-	isBool     bool
+	boolean    bool
 	fieldName  string // for generating helpful errors
 }
 
 // ErrHelp indicates that -h or --help were provided
 var ErrHelp = errors.New("help requested by user")
 
-// The TextUnmarshaler type in reflection form
-var textUnsmarshalerType = reflect.TypeOf([]encoding.TextUnmarshaler{}).Elem()
-
 // MustParse processes command line arguments and exits upon failure
 func MustParse(dest ...interface{}) *Parser {
 	p, err := NewParser(dest...)
@@ -94,33 +90,10 @@ func NewParser(dests ...interface{}) (*Parser, error) {
 			// wait until setScalar because it means that a program with invalid argument
 			// fields will always fail regardless of whether the arguments it recieved happend
 			// to exercise those fields.
-			if !field.Type.Implements(textUnsmarshalerType) {
-				scalarType := field.Type
-				// Look inside pointer types
-				if scalarType.Kind() == reflect.Ptr {
-					scalarType = scalarType.Elem()
-				}
-				// Check for bool
-				if scalarType.Kind() == reflect.Bool {
-					spec.isBool = true
-				}
-				// Look inside slice types
-				if scalarType.Kind() == reflect.Slice {
-					spec.multiple = true
-					scalarType = scalarType.Elem()
-				}
-				// Look inside pointer types (again, in case of []*Type)
-				if scalarType.Kind() == reflect.Ptr {
-					scalarType = scalarType.Elem()
-				}
-
-				// Check for unsupported types
-				switch scalarType.Kind() {
-				case reflect.Array, reflect.Chan, reflect.Func, reflect.Interface,
-					reflect.Map, reflect.Ptr, reflect.Struct,
-					reflect.Complex64, reflect.Complex128:
-					return nil, fmt.Errorf("%s.%s: %s fields are not supported", t.Name(), field.Name, scalarType.Kind())
-				}
+			var parseable bool
+			parseable, spec.boolean, spec.multiple = canParse(field.Type)
+			if !parseable {
+				return nil, fmt.Errorf("%s.%s: %s fields are not supported", t.Name(), field.Name, field.Type.String())
 			}
 
 			// Look at the tag
@@ -264,8 +237,8 @@ func process(specs []*spec, args []string) error {
 		}
 
 		// if it's a flag and it has no value then set the value to true
-		// use isBool because this takes account of TextUnmarshaler
-		if spec.isBool && value == "" {
+		// use boolean because this takes account of TextUnmarshaler
+		if spec.boolean && value == "" {
 			value = "true"
 		}
 
@@ -345,3 +318,38 @@ func setSlice(dest reflect.Value, values []string) error {
 	}
 	return nil
 }
+
+// canParse returns true if the type can be parsed from a string
+func canParse(t reflect.Type) (parseable, boolean, multiple bool) {
+	parseable, boolean = isScalar(t)
+	if parseable {
+		return
+	}
+
+	// Look inside pointer types
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+	// Look inside slice types
+	if t.Kind() == reflect.Slice {
+		multiple = true
+		t = t.Elem()
+	}
+
+	parseable, boolean = isScalar(t)
+	if parseable {
+		return
+	}
+
+	// Look inside pointer types (again, in case of []*Type)
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	parseable, boolean = isScalar(t)
+	if parseable {
+		return
+	}
+
+	return false, false, false
+}

scalar.go

@@ -3,11 +3,57 @@ package arg
 import (
 	"encoding"
 	"fmt"
+	"net"
+	"net/mail"
 	"reflect"
 	"strconv"
 	"time"
 )
 
+// The reflected form of some special types
+var (
+	textUnmarshalerType = reflect.TypeOf([]encoding.TextUnmarshaler{}).Elem()
+	durationType        = reflect.TypeOf(time.Duration(0))
+	mailAddressType     = reflect.TypeOf(mail.Address{})
+	ipType              = reflect.TypeOf(net.IP{})
+	macType             = reflect.TypeOf(net.HardwareAddr{})
+)
+
+// isScalar returns true if the type can be parsed from a single string
+func isScalar(t reflect.Type) (scalar, boolean bool) {
+	// If it implements encoding.TextUnmarshaler then use that
+	if t.Implements(textUnmarshalerType) {
+		// scalar=YES, boolean=NO
+		return true, false
+	}
+
+	// If we have a pointer then dereference it
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	// Check for other special types
+	switch t {
+	case durationType, mailAddressType, ipType, macType:
+		// scalar=YES, boolean=NO
+		return true, false
+	}
+
+	// Fall back to checking the kind
+	switch t.Kind() {
+	case reflect.Bool:
+		// scalar=YES, boolean=YES
+		return true, true
+	case reflect.String, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+		reflect.Float32, reflect.Float64:
+		// scalar=YES, boolean=NO
+		return true, false
+	}
+	// scalar=NO, boolean=NO
+	return false, false
+}
+
 // set a value from a string
 func setScalar(v reflect.Value, s string) error {
 	if !v.CanSet() {
@@ -35,12 +81,30 @@ func setScalar(v reflect.Value, s string) error {
 	// Switch on concrete type
 	switch scalar.(type) {
 	case time.Duration:
-		x, err := time.ParseDuration(s)
+		duration, err := time.ParseDuration(s)
 		if err != nil {
 			return err
 		}
-		v.Set(reflect.ValueOf(x))
+		v.Set(reflect.ValueOf(duration))
 		return nil
+	case mail.Address:
+		addr, err := mail.ParseAddress(s)
+		if err != nil {
+			return err
+		}
+		v.Set(reflect.ValueOf(*addr))
+	case net.IP:
+		ip := net.ParseIP(s)
+		if ip == nil {
+			return fmt.Errorf(`invalid IP address: "%s"`, s)
+		}
+		v.Set(reflect.ValueOf(ip))
+	case net.HardwareAddr:
+		ip, err := net.ParseMAC(s)
+		if err != nil {
+			return err
+		}
+		v.Set(reflect.ValueOf(ip))
 	}
 
 	// Switch on kind so that we can handle derived types

usage.go

@@ -97,7 +97,7 @@ func (p *Parser) WriteHelp(w io.Writer) {
 	}
 
 	// write the list of built in options
-	printOption(w, &spec{isBool: true, long: "help", short: "h", help: "display this help and exit"})
+	printOption(w, &spec{boolean: true, long: "help", short: "h", help: "display this help and exit"})
 }
 
 func printOption(w io.Writer, spec *spec) {
@@ -127,7 +127,7 @@ func printOption(w io.Writer, spec *spec) {
 }
 
 func synopsis(spec *spec, form string) string {
-	if spec.isBool {
+	if spec.boolean {
 		return form
 	}
 	return form + " " + strings.ToUpper(spec.long)