add join function

README.md

@@ -224,6 +224,10 @@ render("{{ last(guests) }} was last.", data); // "Patir was last."
 render("{{ sort([3,2,1]) }}", data); // "[1,2,3]"
 render("{{ sort(guests) }}", data); // "[\"Jeff\", \"Patrick\", \"Tom\"]"
 
+// Join a list with a separator
+render("{{ join([1,2,3], \" + \") }}", data); // "1 + 2 + 3"
+render("{{ join(guests, \", \") }}", data); // "Jeff, Patrick, Tom"
+
 // Round numbers to a given precision
 render("{{ round(3.1415, 0) }}", data); // 3
 render("{{ round(3.1415, 3) }}", data); // 3.142

include/inja/function_storage.hpp

@@ -65,6 +65,7 @@ class FunctionStorage {
     Sort,
     Upper,
     Super,
+    Join,
     Callback,
     ParenLeft,
     ParenRight,
@@ -109,6 +110,7 @@ class FunctionStorage {
     {std::make_pair("upper", 1), FunctionData { Operation::Upper }},
     {std::make_pair("super", 0), FunctionData { Operation::Super }},
     {std::make_pair("super", 1), FunctionData { Operation::Super }},
+    {std::make_pair("join", 2), FunctionData { Operation::Join }},
   };
 
 public:

include/inja/parser.hpp

@@ -81,7 +81,7 @@ class Parser {
     auto function = operator_stack.top();
     operator_stack.pop();
 
-    for (size_t i = 0; i < function->number_args; ++i) {
+    for (int i = 0; i < function->number_args; ++i) {
       function->arguments.insert(function->arguments.begin(), arguments.back());
       arguments.pop_back();
     }

include/inja/renderer.hpp

@@ -528,6 +528,24 @@ class Renderer : public NodeVisitor  {
       json_tmp_stack.push_back(result_ptr);
       json_eval_stack.push(result_ptr.get());
     } break;
+    case Op::Join: {
+      const auto args = get_arguments<2>(node);
+      const auto separator = args[1]->get<std::string>();
+      std::ostringstream os;
+      std::string sep;
+      for (const auto& value : *args[0]) {
+        os << sep;
+        if (value.is_string()) {
+          os << value.get<std::string>(); // otherwise the value is surrounded with ""
+        } else {
+          os << value;
+        }
+        sep = separator;
+      }
+      result_ptr = std::make_shared<json>(os.str());
+      json_tmp_stack.push_back(result_ptr);
+      json_eval_stack.push(result_ptr.get());
+    } break;
     case Op::ParenLeft:
     case Op::ParenRight:
     case Op::None:

single_include/inja/inja.hpp

@@ -1598,6 +1598,7 @@ class FunctionStorage {
     Sort,
     Upper,
     Super,
+    Join,
     Callback,
     ParenLeft,
     ParenRight,
@@ -1642,6 +1643,7 @@ class FunctionStorage {
     {std::make_pair("upper", 1), FunctionData { Operation::Upper }},
     {std::make_pair("super", 0), FunctionData { Operation::Super }},
     {std::make_pair("super", 1), FunctionData { Operation::Super }},
+    {std::make_pair("join", 2), FunctionData { Operation::Join }},
   };
 
 public:
@@ -2916,7 +2918,7 @@ class Parser {
     auto function = operator_stack.top();
     operator_stack.pop();
 
-    for (size_t i = 0; i < function->number_args; ++i) {
+    for (int i = 0; i < function->number_args; ++i) {
       function->arguments.insert(function->arguments.begin(), arguments.back());
       arguments.pop_back();
     }
@@ -4018,6 +4020,24 @@ class Renderer : public NodeVisitor  {
       json_tmp_stack.push_back(result_ptr);
       json_eval_stack.push(result_ptr.get());
     } break;
+    case Op::Join: {
+      const auto args = get_arguments<2>(node);
+      const auto separator = args[1]->get<std::string>();
+      std::ostringstream os;
+      std::string sep;
+      for (const auto& value : *args[0]) {
+        os << sep;
+        if (value.is_string()) {
+          os << value.get<std::string>(); // otherwise the value is surrounded with ""
+        } else {
+          os << value;
+        }
+        sep = separator;
+      }
+      result_ptr = std::make_shared<json>(os.str());
+      json_tmp_stack.push_back(result_ptr);
+      json_eval_stack.push(result_ptr.get());
+    } break;
     case Op::ParenLeft:
     case Op::ParenRight:
     case Op::None:

test/test-functions.cpp

@@ -174,6 +174,11 @@ TEST_CASE("functions") {
                       "[inja.exception.render_error] (at 1:22) variable 'sister' not found");
   }
 
+  SUBCASE("join") {
+    CHECK(env.render("{{ join(names, \" | \") }}", data) == "Jeff | Seb | Peter | Tom");
+    CHECK(env.render("{{ join(vars, \", \") }}", data) == "2, 3, 4, 0, -1, -2, -3");
+  }
+
   SUBCASE("isType") {
     CHECK(env.render("{{ isBoolean(is_happy) }}", data) == "true");
     CHECK(env.render("{{ isBoolean(vars) }}", data) == "false");