Fix typeSwitchVar warnings (#243)

Fixes #242

marshal.go

@@ -530,20 +530,20 @@ func (d *Decoder) valueFromToml(mtype reflect.Type, tval interface{}) (reflect.V
 		return d.unwrapPointer(mtype, tval)
 	}
 
-	switch tval.(type) {
+	switch t := tval.(type) {
 	case *Tree:
 		if isTree(mtype) {
-			return d.valueFromTree(mtype, tval.(*Tree))
+			return d.valueFromTree(mtype, t)
 		}
 		return reflect.ValueOf(nil), fmt.Errorf("Can't convert %v(%T) to a tree", tval, tval)
 	case []*Tree:
 		if isTreeSlice(mtype) {
-			return d.valueFromTreeSlice(mtype, tval.([]*Tree))
+			return d.valueFromTreeSlice(mtype, t)
 		}
 		return reflect.ValueOf(nil), fmt.Errorf("Can't convert %v(%T) to trees", tval, tval)
 	case []interface{}:
 		if isOtherSlice(mtype) {
-			return d.valueFromOtherSlice(mtype, tval.([]interface{}))
+			return d.valueFromOtherSlice(mtype, t)
 		}
 		return reflect.ValueOf(nil), fmt.Errorf("Can't convert %v(%T) to a slice", tval, tval)
 	default:

toml.go

@@ -215,17 +215,15 @@ func (t *Tree) SetPathWithOptions(keys []string, opts SetOptions, value interfac
 
 	var toInsert interface{}
 
-	switch value.(type) {
+	switch v := value.(type) {
 	case *Tree:
-		tt := value.(*Tree)
-		tt.comment = opts.Comment
+		v.comment = opts.Comment
 		toInsert = value
 	case []*Tree:
 		toInsert = value
 	case *tomlValue:
-		tt := value.(*tomlValue)
-		tt.comment = opts.Comment
-		toInsert = tt
+		v.comment = opts.Comment
+		toInsert = v
 	default:
 		toInsert = &tomlValue{value: value, comment: opts.Comment, commented: opts.Commented, multiline: opts.Multiline}
 	}
@@ -278,17 +276,15 @@ func (t *Tree) SetPathWithComment(keys []string, comment string, commented bool,
 
 	var toInsert interface{}
 
-	switch value.(type) {
+	switch v := value.(type) {
 	case *Tree:
-		tt := value.(*Tree)
-		tt.comment = comment
+		v.comment = comment
 		toInsert = value
 	case []*Tree:
 		toInsert = value
 	case *tomlValue:
-		tt := value.(*tomlValue)
-		tt.comment = comment
-		toInsert = tt
+		v.comment = comment
+		toInsert = v
 	default:
 		toInsert = &tomlValue{value: value, comment: comment, commented: commented}
 	}