Add append feature for arrays

README.md

@@ -191,6 +191,14 @@ Arrays in Plush will get translated to the Go type `[]interface{}` when used.
 []interface{}{ 1, 2, "three", "four", h }
 ```
 
+Arrays in plush can be appended using the following format:
+
+```erb
+<% let a = [1, 2, "three", "four", h] %> <% a = a + "hello world"%>
+```
+
+If the array passed to plush is not of type `[]interface{}` and an attempt is made to append a value with a data type that does not match the underlying array type, an error will be returned. 
+
 ## For Loops
 
 There are three different types that can be looped over: maps, arrays/slices, and iterators. The format for them all looks the same:

compiler.go

@@ -499,11 +499,36 @@ func (c *compiler) evalInfixExpression(node *ast.InfixExpression) (interface{},
 		}
 	case bool:
 		return c.boolsOperator(lres, rres, node.Operator)
+	default:
+		if reflect.TypeOf(t).Kind() == reflect.Slice || reflect.TypeOf(t).Kind() == reflect.Array {
+			return c.arrayOperator(lres, rres, node.Operator)
+		}
 	}
 
 	return nil, fmt.Errorf("unable to operate (%s) on %T and %T ", node.Operator, lres, rres)
 }
 
+func (c *compiler) arrayOperator(l interface{}, r interface{}, op string) (interface{}, error) {
+	var err error
+	switch op {
+	case "+":
+		elemType := reflect.TypeOf(l).Elem()
+		if elemType.Kind() != reflect.Interface {
+			t := reflect.ValueOf(r).Type()
+			if elemType != t {
+				err = fmt.Errorf("cannot append '%v' (untyped %s constant) as %s value in assignment", r, t, elemType)
+			}
+		}
+		if err == nil {
+			return reflect.Append(reflect.ValueOf(l), reflect.ValueOf(r)), nil
+		}
+	default:
+		err = fmt.Errorf("unkown operator (%s) on %T and %T ", op, l, r)
+	}
+
+	return nil, err
+}
+
 func (c *compiler) nilsOperator(l interface{}, r interface{}, op string) (interface{}, error) {
 	switch op {
 	case "!=":

variables_test.go

@@ -2,6 +2,7 @@ package plush_test
 
 import (
 	"html/template"
+	"log"
 	"strings"
 	"testing"
 
@@ -174,6 +175,37 @@ func Test_Render_Let_ArrayAsssign_AssignableToArrayInterface(t *testing.T) {
 	r.NoError(err)
 }
 
+func Test_Render_AppendArray_WithTypeIntArrayTypeString(t *testing.T) {
+	r := require.New(t)
+	ctx := plush.NewContext()
+
+	ctx.Set("myArray", []string{"a", "b"})
+	input := `<% let a = myArray %><% a = a + 1 %><%= a %>`
+	_, err := plush.Render(input, ctx)
+	r.Error(err)
+	r.Contains(err.Error(), "cannot append '1' (untyped int constant) as string value in assignment")
+}
+
+func Test_Render_AppendArray_CreatedInPlush(t *testing.T) {
+	r := require.New(t)
+
+	input := `<% let a = [1,2,"HelloWorld"] %><% a = a + 2.2 %><%= a %>`
+	s, err := plush.Render(input, plush.NewContext())
+	r.NoError(err)
+	r.Equal(s, "12HelloWorld2.2")
+}
+func Test_Render_AppendArray_WithTypeInterface(t *testing.T) {
+	r := require.New(t)
+	ctx := plush.NewContext()
+
+	ctx.Set("myArray", []interface{}{"a", "b"})
+	input := `<% let a = myArray %><% a = a + 1 %><%= a %>`
+	s, err := plush.Render(input, ctx)
+	log.Println(s)
+	r.NoError(err)
+	r.Equal("ab1", s)
+}
+
 type Category1 struct {
 	Products []Product1
 }