diff --git a/src/ArduinoJson/Strings/ArduinoStringAdapter.hpp b/src/ArduinoJson/Strings/ArduinoStringAdapter.hpp
index 5850a3b0..ac7bbdc3 100644
--- a/src/ArduinoJson/Strings/ArduinoStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/ArduinoStringAdapter.hpp
@@ -7,6 +7,7 @@
 #include <WString.h>
 
 #include <ArduinoJson/Polyfills/safe_strcmp.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -39,17 +40,11 @@ class ArduinoStringAdapter {
     return compare(expected) == 0;
   }
 
-  const char* data() const {
-    return _str->c_str();
-  }
-
   size_t size() const {
     return _str->length();
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef storage_policy::store_by_copy storage_policy;
 
  private:
   const ::String* _str;
diff --git a/src/ArduinoJson/Strings/ConstRamStringAdapter.hpp b/src/ArduinoJson/Strings/ConstRamStringAdapter.hpp
index a7176b08..407f584d 100644
--- a/src/ArduinoJson/Strings/ConstRamStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/ConstRamStringAdapter.hpp
@@ -8,6 +8,7 @@
 #include <string.h>  // strcmp
 
 #include <ArduinoJson/Polyfills/safe_strcmp.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -27,11 +28,6 @@ class ConstRamStringAdapter {
     return !_str;
   }
 
-  template <typename TMemoryPool>
-  char* save(TMemoryPool*) const {
-    return 0;
-  }
-
   size_t size() const {
     if (!_str)
       return 0;
@@ -42,9 +38,7 @@ class ConstRamStringAdapter {
     return _str;
   }
 
-  bool isStatic() const {
-    return true;
-  }
+  typedef storage_policy::store_by_address storage_policy;
 
  protected:
   const char* _str;
diff --git a/src/ArduinoJson/Strings/FlashStringAdapter.hpp b/src/ArduinoJson/Strings/FlashStringAdapter.hpp
index 74bc3950..328f040f 100644
--- a/src/ArduinoJson/Strings/FlashStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/FlashStringAdapter.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Polyfills/pgmspace.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -40,19 +41,13 @@ class FlashStringAdapter {
     return dup;
   }
 
-  const char* data() const {
-    return 0;
-  }
-
   size_t size() const {
     if (!_str)
       return 0;
     return strlen_P(reinterpret_cast<const char*>(_str));
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef storage_policy::store_by_copy storage_policy;
 
  private:
   const __FlashStringHelper* _str;
diff --git a/src/ArduinoJson/Strings/RamStringAdapter.hpp b/src/ArduinoJson/Strings/RamStringAdapter.hpp
index 6909bf98..05db2e84 100644
--- a/src/ArduinoJson/Strings/RamStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/RamStringAdapter.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Strings/ConstRamStringAdapter.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -22,9 +23,7 @@ class RamStringAdapter : public ConstRamStringAdapter {
     return dup;
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef ARDUINOJSON_NAMESPACE::storage_policy::store_by_copy storage_policy;
 };
 
 template <typename TChar>
diff --git a/src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp b/src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp
index 48fe2855..41a6cf6d 100644
--- a/src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/SizedFlashStringAdapter.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -45,9 +46,7 @@ class SizedFlashStringAdapter {
     return _size;
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef storage_policy::store_by_copy storage_policy;
 
  private:
   const __FlashStringHelper* _str;
diff --git a/src/ArduinoJson/Strings/SizedRamStringAdapter.hpp b/src/ArduinoJson/Strings/SizedRamStringAdapter.hpp
index 04c5630b..911f4af6 100644
--- a/src/ArduinoJson/Strings/SizedRamStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/SizedRamStringAdapter.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 #include <string.h>  // strcmp
 
@@ -39,9 +40,7 @@ class SizedRamStringAdapter {
     return _size;
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef storage_policy::store_by_copy storage_policy;
 
  private:
   const char* _str;
diff --git a/src/ArduinoJson/Strings/StlStringAdapter.hpp b/src/ArduinoJson/Strings/StlStringAdapter.hpp
index 617e8231..defec413 100644
--- a/src/ArduinoJson/Strings/StlStringAdapter.hpp
+++ b/src/ArduinoJson/Strings/StlStringAdapter.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 #include <string>
 
@@ -39,17 +40,11 @@ class StlStringAdapter {
     return *_str == expected;
   }
 
-  const char* data() const {
-    return _str->data();
-  }
-
   size_t size() const {
     return _str->size();
   }
 
-  bool isStatic() const {
-    return false;
-  }
+  typedef storage_policy::store_by_copy storage_policy;
 
  private:
   const TString* _str;
diff --git a/src/ArduinoJson/Strings/StoragePolicy.hpp b/src/ArduinoJson/Strings/StoragePolicy.hpp
new file mode 100644
index 00000000..ea9adcf4
--- /dev/null
+++ b/src/ArduinoJson/Strings/StoragePolicy.hpp
@@ -0,0 +1,15 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+namespace ARDUINOJSON_NAMESPACE {
+
+namespace storage_policy {
+struct store_by_address {};
+struct store_by_copy {};
+struct decide_at_runtime {};
+}  // namespace storage_policy
+
+}  // namespace ARDUINOJSON_NAMESPACE
diff --git a/src/ArduinoJson/Strings/String.hpp b/src/ArduinoJson/Strings/String.hpp
index 1cc42068..eeced00c 100644
--- a/src/ArduinoJson/Strings/String.hpp
+++ b/src/ArduinoJson/Strings/String.hpp
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Strings/ConstRamStringAdapter.hpp>
+#include <ArduinoJson/Strings/StoragePolicy.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -36,6 +37,8 @@ class String {
     return strcmp(lhs._data, rhs._data) == 0;
   }
 
+  typedef storage_policy::decide_at_runtime storage_policy;
+
  private:
   const char* _data;
   bool _isStatic;
diff --git a/src/ArduinoJson/Variant/SlotFunctions.hpp b/src/ArduinoJson/Variant/SlotFunctions.hpp
index fb16177b..ef75a94d 100644
--- a/src/ArduinoJson/Variant/SlotFunctions.hpp
+++ b/src/ArduinoJson/Variant/SlotFunctions.hpp
@@ -13,17 +13,39 @@ template <typename TAdaptedString>
 inline bool slotSetKey(VariantSlot* var, TAdaptedString key, MemoryPool* pool) {
   if (!var)
     return false;
+  return slotSetKey(var, key, pool, typename TAdaptedString::storage_policy());
+}
+
+template <typename TAdaptedString>
+inline bool slotSetKey(VariantSlot* var, TAdaptedString key, MemoryPool* pool,
+                       storage_policy::decide_at_runtime) {
   if (key.isStatic()) {
-    var->setLinkedKey(make_not_null(key.data()));
+    return slotSetKey(var, key, pool, storage_policy::store_by_address());
   } else {
-    const char* dup = key.save(pool);
-    if (!dup)
-      return false;
-    var->setOwnedKey(make_not_null(dup));
+    return slotSetKey(var, key, pool, storage_policy::store_by_copy());
   }
   return true;
 }
 
+template <typename TAdaptedString>
+inline bool slotSetKey(VariantSlot* var, TAdaptedString key, MemoryPool*,
+                       storage_policy::store_by_address) {
+  ARDUINOJSON_ASSERT(var);
+  var->setLinkedKey(make_not_null(key.data()));
+  return true;
+}
+
+template <typename TAdaptedString>
+inline bool slotSetKey(VariantSlot* var, TAdaptedString key, MemoryPool* pool,
+                       storage_policy::store_by_copy) {
+  const char* dup = key.save(pool);
+  if (!dup)
+    return false;
+  ARDUINOJSON_ASSERT(var);
+  var->setOwnedKey(make_not_null(dup));
+  return true;
+}
+
 inline size_t slotSize(const VariantSlot* var) {
   size_t n = 0;
   while (var) {