add first and last function

README.md

@@ -167,9 +167,13 @@ render("Hello {{ lower(neighbour) }}!", data); // "Hello peter!"
 // Range function, useful for loops
 render("{% for i in range(4) %}{{ index1 }}{% endfor %}", data); // "1234"
 
-// Length function (but please don't combine with range, use list directly...)
+// Length function (please don't combine with range, use list directly...)
 render("I count {{ length(guests) }} guests.", data); // "I count 3 guests."
 
+// Get first and last element in a list
+render("{{ first(guests) }} was first.", data); // "Jeff was first."
+render("{{ last(guests) }} was last.", data); // "Tom was last."
+
 // Round numbers to a given precision
 render({{ round(3.1415, 0) }}, data); // 3
 render({{ round(3.1415, 3) }}, data); // 3.142

src/inja.hpp

@@ -243,6 +243,8 @@ struct Parsed {
 		Lower,
 		Range,
 		Length,
+		First,
+		Last,
 		Round,
 		DivisibleBy,
 		Odd,
@@ -356,6 +358,14 @@ public:
 				const std::vector<json> list = eval_expression<std::vector<json>>(element.args[0], data);
 				return list.size();
 			}
+			case Parsed::Function::First: {
+				const std::vector<json> list = eval_expression<std::vector<json>>(element.args[0], data);
+				return list.front();
+			}
+			case Parsed::Function::Last: {
+				const std::vector<json> list = eval_expression<std::vector<json>>(element.args[0], data);
+				return list.back();
+			}
 			case Parsed::Function::Round: {
 				const double number = eval_expression<double>(element.args[0], data);
 				const int precision = eval_expression<int>(element.args[1], data);
@@ -548,6 +558,8 @@ public:
 		{Parsed::Function::Lower, function_regex("lower", 1)},
 		{Parsed::Function::Range, function_regex("range", 1)},
 		{Parsed::Function::Length, function_regex("length", 1)},
+		{Parsed::Function::First, function_regex("first", 1)},
+		{Parsed::Function::Last, function_regex("last", 1)},
 		{Parsed::Function::Round, function_regex("round", 2)},
 		{Parsed::Function::DivisibleBy, function_regex("divisibleBy", 2)},
 		{Parsed::Function::Odd, function_regex("odd", 1)},

test/src/unit-renderer.cpp

@@ -99,6 +99,16 @@ TEST_CASE("functions") {
 		// CHECK_THROWS_WITH( env.render("{{ length(5) }}", data), "[json.exception.type_error.302] type must be array, but is number" );
 	}
 
+	SECTION("first") {
+		CHECK( env.render("{{ first(names) }}", data) == "Jeff" );
+		// CHECK_THROWS_WITH( env.render("{{ length(5) }}", data), "[json.exception.type_error.302] type must be array, but is number" );
+	}
+
+	SECTION("last") {
+		CHECK( env.render("{{ last(names) }}", data) == "Tom" );
+		// CHECK_THROWS_WITH( env.render("{{ length(5) }}", data), "[json.exception.type_error.302] type must be array, but is number" );
+	}
+
 	SECTION("round") {
 		CHECK( env.render("{{ round(4, 0) }}", data) == "4.0" );
 		CHECK( env.render("{{ round(temperature, 2) }}", data) == "25.68" );