1 files changed, 154 insertions, 0 deletions
diff --git a/scalar.go b/scalar.go
new file mode 100644
index 0000000..663f143
--- /dev/null
+++ b/scalar.go
@@ -0,0 +1,154 @@
+// Package scalar parses strings into values of scalar type.
+
+package scalar
+
+import (
+	"encoding"
+	"errors"
+	"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{})
+)
+
+var (
+	errNotSettable    = errors.New("value is not settable")
+	errPtrNotSettable = errors.New("value is a nil pointer and is not settable")
+)
+
+// Parse assigns a value to v by parsing s.
+func Parse(dest interface{}, s string) error {
+	return ParseValue(reflect.ValueOf(dest), s)
+}
+
+// ParseValue assigns a value to v by parsing s.
+func ParseValue(v reflect.Value, s string) error {
+	// If we have a nil pointer then allocate a new object
+	if v.Kind() == reflect.Ptr && v.IsNil() {
+		if !v.CanSet() {
+			return errPtrNotSettable
+		}
+
+		v.Set(reflect.New(v.Type().Elem()))
+	}
+
+	// If it implements encoding.TextUnmarshaler then use that
+	if scalar, ok := v.Interface().(encoding.TextUnmarshaler); ok {
+		return scalar.UnmarshalText([]byte(s))
+	}
+
+	// If we have a pointer then dereference it
+	if v.Kind() == reflect.Ptr {
+		v = v.Elem()
+	}
+
+	if !v.CanSet() {
+		return errNotSettable
+	}
+
+	// Switch on concrete type
+	switch scalar := v.Interface(); scalar.(type) {
+	case time.Duration:
+		duration, err := time.ParseDuration(s)
+		if err != nil {
+			return err
+		}
+		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))
+		return nil
+	case net.IP:
+		ip := net.ParseIP(s)
+		if ip == nil {
+			return fmt.Errorf(`invalid IP address: "%s"`, s)
+		}
+		v.Set(reflect.ValueOf(ip))
+		return nil
+	case net.HardwareAddr:
+		ip, err := net.ParseMAC(s)
+		if err != nil {
+			return err
+		}
+		v.Set(reflect.ValueOf(ip))
+		return nil
+	}
+
+	// Switch on kind so that we can handle derived types
+	switch v.Kind() {
+	case reflect.String:
+		v.SetString(s)
+	case reflect.Bool:
+		x, err := strconv.ParseBool(s)
+		if err != nil {
+			return err
+		}
+		v.SetBool(x)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		x, err := strconv.ParseInt(s, 10, v.Type().Bits())
+		if err != nil {
+			return err
+		}
+		v.SetInt(x)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		x, err := strconv.ParseUint(s, 10, v.Type().Bits())
+		if err != nil {
+			return err
+		}
+		v.SetUint(x)
+	case reflect.Float32, reflect.Float64:
+		x, err := strconv.ParseFloat(s, v.Type().Bits())
+		if err != nil {
+			return err
+		}
+		v.SetFloat(x)
+	default:
+		return fmt.Errorf("cannot parse into %v", v.Type())
+	}
+	return nil
+}
+
+// CanParse returns true if the type can be parsed from a string.
+func CanParse(t reflect.Type) bool {
+	// If it implements encoding.TextUnmarshaler then use that
+	if t.Implements(textUnmarshalerType) {
+		return true
+	}
+
+	// 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:
+		return true
+	}
+
+	// Fall back to checking the kind
+	switch t.Kind() {
+	case reflect.Bool:
+		return 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.Uintptr,
+		reflect.Float32, reflect.Float64:
+		return true
+	}
+	return false
+}