diff --git a/runtime/alloc.cpp b/runtime/alloc.cpp
new file mode 100644
index 0000000..b1c587e
--- /dev/null
+++ b/runtime/alloc.cpp
@@ -0,0 +1,16 @@
+#include "alloc.hpp"
+#include <format>
+#include <iostream>
+
+using namespace sliger::heap;
+
+auto Array::at(int32_t index) & -> Value&
+{
+    if (index >= static_cast<int32_t>(this->values.size()) || index < 0) {
+        std::cout << std::format(
+            "index not in range, expected to be in range (0..{}), got: {}",
+            this->values.size(), index);
+        exit(1);
+    }
+    return values.at(static_cast<size_t>(index));
+}
diff --git a/runtime/alloc.hpp b/runtime/alloc.hpp
index a4bc9fe..b75f515 100644
--- a/runtime/alloc.hpp
+++ b/runtime/alloc.hpp
@@ -13,13 +13,8 @@ namespace sliger::heap {
 
 struct Array {
     std::vector<Value> values;
-    inline auto at(int32_t index)& -> Value& {
-        if (index >= static_cast<int32_t>(this->values.size()) || index < 0) {
-            std::cout << std::format("index not in range, expected to be in range (0..{}), got: {}", this->values.size(), index);
-            exit(1);
-        }
-        return values.at(index);
-    }
+
+    auto at(int32_t index) & -> Value&;
 };
 
 struct Struct {
@@ -40,9 +35,21 @@ template <> struct AllocTypeType<AllocType::Struct> { using Type = Struct; };
 // clang-format on
 
 struct AllocItem {
-    AllocItem(Value&& val) : type(AllocType::Value), value(val) {}
-    AllocItem(Array&& val) : type(AllocType::Array), value(val) {}
-    AllocItem(Struct&& val) : type(AllocType::Struct), value(val) {}
+    AllocItem(Value&& val)
+        : type(AllocType::Value)
+        , value(val)
+    {
+    }
+    AllocItem(Array&& val)
+        : type(AllocType::Array)
+        , value(val)
+    {
+    }
+    AllocItem(Struct&& val)
+        : type(AllocType::Struct)
+        , value(val)
+    {
+    }
 
     template <AllocType AT> inline auto as() & -> AllocTypeType<AT>::Type&
     {
@@ -65,26 +72,25 @@ struct AllocItem {
             std::get<typename AllocTypeType<AT>::Type>(this->value));
     }
 
-    inline auto as_value() & -> Value& {
+    inline auto as_value() & -> Value& { return std::get<Value>(this->value); }
+    inline auto as_value() const& -> const Value&
+    {
         return std::get<Value>(this->value);
     }
-    inline auto as_value() const & -> const Value& {
-        return std::get<Value>(this->value);
-    }
-    inline auto as_array() & -> Array& {
+    inline auto as_array() & -> Array& { return std::get<Array>(this->value); }
+    inline auto as_array() const& -> const Array&
+    {
         return std::get<Array>(this->value);
     }
-    inline auto as_array() const & -> const Array& {
-        return std::get<Array>(this->value);
-    }
-    inline auto as_struct() & -> Struct& {
+    inline auto as_struct() & -> Struct&
+    {
         return std::get<Struct>(this->value);
     }
-    inline auto as_struct() const & -> const Struct& {
+    inline auto as_struct() const& -> const Struct&
+    {
         return std::get<Struct>(this->value);
     }
 
-
     AllocType type;
     std::variant<Value, Array, Struct> value;
 };
diff --git a/runtime/value.cpp b/runtime/value.cpp
index 12a259a..34d0c4a 100644
--- a/runtime/value.cpp
+++ b/runtime/value.cpp
@@ -4,6 +4,17 @@
 
 using namespace sliger;
 
+auto String::at(int32_t index) -> int32_t
+{
+    if (index >= static_cast<int32_t>(this->value.length()) || index < 0) {
+        std::cout << std::format(
+            "index not in range, expected to be in range (0..{}), got: {}",
+            this->value.length() - 1, index);
+        exit(1);
+    }
+    return this->value.at(static_cast<size_t>(index));
+}
+
 auto Value::to_string() const -> std::string
 {
     switch (this->m_type) {
diff --git a/runtime/value.hpp b/runtime/value.hpp
index e1e3d52..02a8181 100644
--- a/runtime/value.hpp
+++ b/runtime/value.hpp
@@ -68,13 +68,8 @@ struct Bool {
 };
 struct String {
     std::string value;
-    inline auto at(int32_t index) -> int32_t {
-        if (index >= static_cast<int32_t>(this->value.length()) || index < 0) {
-            std::cout << std::format("index not in range, expected to be in range (0..{}), got: {}", this->value.length()-1, index);
-            exit(1);
-        }
-        return this->value.at(index);
-    }
+
+    auto at(int32_t index) -> int32_t;
 };
 struct Ptr {
     uint32_t value;