Add string join and title function (#127)

* Add string join and title function

Author: lixingwang

function/string/descriptor.json

@@ -283,6 +283,26 @@
         "type": "int"
       }
     },
+    {
+      "name": "join",
+      "description": "Converts an array to its string representation and concatenates its elements using the specified separator between each element",
+      "example": "string.join(array.create(\"a\", \"b\"), \"-\") => a-b",
+      "args": [
+        {
+          "name": "items",
+          "type": "array",
+          "valueType": "any"
+        },
+        {
+          "name": "separator",
+          "type": "string"
+        }
+      ],
+      "return": {
+        "type": "array",
+        "valueType": "any"
+      }
+    },
     {
       "name": "lastIndex",
       "description": "LastIndex returns the index of the last instance of substring in inputstring, or -1 if substring is not present in inputstring. string.lastIndex(\"go gopher\", \"go\")",
@@ -367,6 +387,20 @@
         "type": "string"
       }
     },
+    {
+      "name": "toTitleCase",
+      "description": "returns the string to capitalize the first letter of every word",
+      "example": "string.toTitleCase(\"hello world\") => Hello World",
+      "args": [
+        {
+          "name": "str",
+          "type": "string"
+        },
+      ],
+      "return": {
+        "type": "string"
+      }
+    },
     {
       "name": "toLower",
       "description": "toLower returns a copy of inputstring with all Unicode letters mapped to their lower case.  ",

function/string/join.go

@@ -0,0 +1,45 @@
+package string
+
+import (
+	"fmt"
+	"github.com/project-flogo/core/data"
+	"github.com/project-flogo/core/data/coerce"
+	"github.com/project-flogo/core/data/expression/function"
+	"strings"
+)
+
+func init() {
+	_ = function.Register(&fnJoin{})
+}
+
+type fnJoin struct {
+}
+
+func (fnJoin) Name() string {
+	return "join"
+}
+
+func (fnJoin) Sig() (paramTypes []data.Type, isVariadic bool) {
+	return []data.Type{data.TypeArray, data.TypeString}, false
+}
+
+func (fnJoin) Eval(params ...interface{}) (interface{}, error) {
+	a, err := coerce.ToArray(params[0])
+	if err != nil {
+		return nil, fmt.Errorf("error converting string.join first argument [%+v] to array: %s", params[0], err.Error())
+	}
+	str, err := coerce.ToString(params[1])
+	if err != nil {
+		return nil, fmt.Errorf("error converting string.join second argument [%+v] to string: %s", params[0], err.Error())
+	}
+	return strings.Join(toStringArray(a), str), nil
+}
+
+func toStringArray(array []interface{}) []string {
+	var tmpArray []string
+	for _, a := range array {
+		str, _ := coerce.ToString(a)
+		tmpArray = append(tmpArray, str)
+	}
+	return tmpArray
+}

function/string/join_test.go

@@ -0,0 +1,14 @@
+package string
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestFnJoin_Eval(t *testing.T) {
+	f := fnJoin{}
+	var a = []string{"abc", "dddd", "cccc"}
+	v, err := f.Eval(a, "-")
+	assert.Nil(t, err)
+	assert.Equal(t, "abc-dddd-cccc", v)
+}

function/string/title.go

@@ -0,0 +1,32 @@
+package string
+
+import (
+	"fmt"
+	"github.com/project-flogo/core/data"
+	"github.com/project-flogo/core/data/coerce"
+	"github.com/project-flogo/core/data/expression/function"
+	"strings"
+)
+
+func init() {
+	_ = function.Register(&fnTitle{})
+}
+
+type fnTitle struct {
+}
+
+func (fnTitle) Name() string {
+	return "toTitleCase"
+}
+
+func (fnTitle) Sig() (paramTypes []data.Type, isVariadic bool) {
+	return []data.Type{data.TypeString}, false
+}
+
+func (fnTitle) Eval(params ...interface{}) (interface{}, error) {
+	str, err := coerce.ToString(params[0])
+	if err != nil {
+		return nil, fmt.Errorf("error converting string.toTitleCase's argument [%+v] to string: %s", params[0], err.Error())
+	}
+	return strings.Title(str), nil
+}

function/string/title_test.go

@@ -0,0 +1,14 @@
+package string
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestFnTitle_Eval(t *testing.T) {
+	f := fnTitle{}
+	str := "hello world"
+	v, err := f.Eval(str)
+	assert.Nil(t, err)
+	assert.Equal(t, "Hello World", v)
+}