Merge pull request #30 from alexflint/scalar_pointers

add support for pointers and TextUnmarshaler

1 files changed, 37 insertions, 20 deletions

diff --git a/parse.go b/parse.go
index 39eb52c..3895ce9 100644
--- a/parse.go
+++ b/parse.go
@@ -1,6 +1,7 @@
 package arg
 
 import (
+	"encoding"
 	"errors"
 	"fmt"
 	"os"
@@ -20,11 +21,15 @@ type spec struct {
 	env        string
 	wasPresent bool
 	isBool     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...)
@@ -80,31 +85,42 @@ func NewParser(dests ...interface{}) (*Parser, error) {
 			}
 
 			spec := spec{
-				long: strings.ToLower(field.Name),
-				dest: v.Field(i),
+				long:      strings.ToLower(field.Name),
+				dest:      v.Field(i),
+				fieldName: t.Name() + "." + field.Name,
 			}
 
-			// Get the scalar type for this field
-			scalarType := field.Type
-			if scalarType.Kind() == reflect.Slice {
-				spec.multiple = true
-				scalarType = scalarType.Elem()
+			// Check whether this field is supported. It's good to do this here rather than
+			// 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())
-			}
 
-			// Specify that it is a bool for usage
-			if scalarType.Kind() == reflect.Bool {
-				spec.isBool = true
+				// 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())
+				}
 			}
 
 			// Look at the tag
@@ -248,7 +264,8 @@ func process(specs []*spec, args []string) error {
 		}
 
 		// if it's a flag and it has no value then set the value to true
-		if spec.dest.Kind() == reflect.Bool && value == "" {
+		// use isBool because this takes account of TextUnmarshaler
+		if spec.isBool && value == "" {
 			value = "true"
 		}