diff --git a/src/variables/duration.h b/src/variables/duration.h
index e9a51a0b..83f02cb3 100644
--- a/src/variables/duration.h
+++ b/src/variables/duration.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class Duration : public Variable {
  public:
-    explicit Duration(std::string _name)
+    explicit Duration(const std::string &_name)
         : Variable(_name),
         m_retName("DURATION") { }
 
diff --git a/src/variables/env.h b/src/variables/env.h
index 2e97c93f..3b5e9f6e 100644
--- a/src/variables/env.h
+++ b/src/variables/env.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class Env : public Variable {
  public:
-    explicit Env(std::string _name)
+    explicit Env(const std::string &_name)
         : Variable(_name) { }
 
     void evaluate(Transaction *transaction,
diff --git a/src/variables/global.h b/src/variables/global.h
index dac0432b..66710526 100644
--- a/src/variables/global.h
+++ b/src/variables/global.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Global_DictElement : public Variable {
  public:
-    explicit Global_DictElement(std::string dictElement)
+    explicit Global_DictElement(const std::string &dictElement)
         : Variable("GLOBAL:" + dictElement),
         m_dictElement("GLOBAL:" + dictElement) { }
 
@@ -67,7 +67,7 @@ class Global_NoDictElement : public Variable {
 
 class Global_DictElementRegexp : public VariableRegex {
  public:
-    explicit Global_DictElementRegexp(std::string dictElement)
+    explicit Global_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("GLOBAL", dictElement),
         m_dictElement(dictElement) { }
 
@@ -100,13 +100,13 @@ class Global_DynamicElement : public Variable {
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_global_collection->del(k,
             t->m_collections.m_global_collection_key,
             t->m_rules->m_secWebAppId.m_value);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
+    static void storeOrUpdateFirst(Transaction *t, std::string var,
         std::string value) {
         t->m_collections.m_global_collection->storeOrUpdateFirst(
             var, t->m_collections.m_global_collection_key,
diff --git a/src/variables/highest_severity.h b/src/variables/highest_severity.h
index 42c602d3..6b5d61cb 100644
--- a/src/variables/highest_severity.h
+++ b/src/variables/highest_severity.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class HighestSeverity : public Variable {
  public:
-    explicit HighestSeverity(std::string _name)
+    explicit HighestSeverity(const std::string &_name)
         : Variable(_name)
     { }
 
diff --git a/src/variables/ip.h b/src/variables/ip.h
index 40f43ac4..d1ee2c05 100644
--- a/src/variables/ip.h
+++ b/src/variables/ip.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Ip_DictElement : public Variable {
  public:
-    explicit Ip_DictElement(std::string dictElement)
+    explicit Ip_DictElement(const std::string &dictElement)
         : Variable("IP:" + dictElement),
         m_dictElement("IP:" + dictElement) { }
 
@@ -67,7 +67,7 @@ class Ip_NoDictElement : public Variable {
 
 class Ip_DictElementRegexp : public VariableRegex {
  public:
-    explicit Ip_DictElementRegexp(std::string dictElement)
+    explicit Ip_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("IP", dictElement),
         m_dictElement(dictElement) { }
 
@@ -99,14 +99,14 @@ class Ip_DynamicElement : public Variable {
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_ip_collection->del(k,
             t->m_collections.m_ip_collection_key,
             t->m_rules->m_secWebAppId.m_value);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
-        std::string value) {
+    static void storeOrUpdateFirst(Transaction *t, const std::string &var,
+        const std::string &value) {
         t->m_collections.m_ip_collection->storeOrUpdateFirst(
             var, t->m_collections.m_ip_collection_key,
             t->m_rules->m_secWebAppId.m_value,
diff --git a/src/variables/modsec_build.h b/src/variables/modsec_build.h
index 556cc413..561a79d6 100644
--- a/src/variables/modsec_build.h
+++ b/src/variables/modsec_build.h
@@ -32,7 +32,7 @@ namespace variables {
 
 class ModsecBuild : public Variable {
  public:
-    explicit ModsecBuild(std::string _name)
+    explicit ModsecBuild(const std::string &_name)
         : Variable(_name),
         m_retName("MODSEC_BUILD") {
         std::ostringstream ss;
diff --git a/src/variables/remote_user.h b/src/variables/remote_user.h
index 226f776c..cc0d565d 100644
--- a/src/variables/remote_user.h
+++ b/src/variables/remote_user.h
@@ -32,7 +32,7 @@ namespace variables {
 
 class RemoteUser : public Variable {
  public:
-    explicit RemoteUser(std::string _name)
+    explicit RemoteUser(const std::string &_name)
         : Variable(_name),
         m_retName("REMOTE_USER") { }
 
diff --git a/src/variables/resource.h b/src/variables/resource.h
index 14fc5e98..c9e3b399 100644
--- a/src/variables/resource.h
+++ b/src/variables/resource.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Resource_DictElement : public Variable {
  public:
-    explicit Resource_DictElement(std::string dictElement)
+    explicit Resource_DictElement(const std::string &dictElement)
         : Variable("RESOURCE:" + dictElement),
         m_dictElement("RESOURCE:" + dictElement) { }
 
@@ -67,7 +67,7 @@ class Resource_NoDictElement : public Variable {
 
 class Resource_DictElementRegexp : public VariableRegex {
  public:
-    explicit Resource_DictElementRegexp(std::string dictElement)
+    explicit Resource_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("RESOURCE:", dictElement),
         m_dictElement(dictElement) { }
 
@@ -99,14 +99,14 @@ class Resource_DynamicElement : public Variable {
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_resource_collection->del(k,
             t->m_collections.m_resource_collection_key,
             t->m_rules->m_secWebAppId.m_value);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
-        std::string value) {
+    static void storeOrUpdateFirst(Transaction *t, const std::string &var,
+        const std::string &value) {
         t->m_collections.m_resource_collection->storeOrUpdateFirst(
             var, t->m_collections.m_resource_collection_key,
             t->m_rules->m_secWebAppId.m_value, value);
diff --git a/src/variables/rule.h b/src/variables/rule.h
index 4f58113d..7855da50 100644
--- a/src/variables/rule.h
+++ b/src/variables/rule.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Rule_DictElement : public VariableDictElement { \
  public:
-    explicit Rule_DictElement(std::string dictElement)
+    explicit Rule_DictElement(const std::string &dictElement)
         : VariableDictElement(std::string("RULE"), dictElement) { }
 
     static void id(Transaction *t,
@@ -194,7 +194,7 @@ class Rule_DictElement : public VariableDictElement { \
 
 class Rule_DictElementRegexp : public VariableRegex {
  public:
-    explicit Rule_DictElementRegexp(std::string regex)
+    explicit Rule_DictElementRegexp(const std::string &regex)
         : VariableRegex("RULE", regex) { }
 
     void evaluate(Transaction *t,
diff --git a/src/variables/session.h b/src/variables/session.h
index a0257d62..e0e0c4df 100644
--- a/src/variables/session.h
+++ b/src/variables/session.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Session_DictElement : public Variable {
  public:
-    explicit Session_DictElement(std::string dictElement)
+    explicit Session_DictElement(const std::string &dictElement)
         : Variable("SESSION:" + dictElement),
         m_dictElement("SESSION:" + dictElement) { }
 
@@ -67,7 +67,7 @@ class Session_NoDictElement : public Variable {
 
 class Session_DictElementRegexp : public VariableRegex {
  public:
-    explicit Session_DictElementRegexp(std::string dictElement)
+    explicit Session_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("SESSION", dictElement),
         m_dictElement(dictElement) { }
 
@@ -99,14 +99,14 @@ class Session_DynamicElement : public Variable {
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_session_collection->del(k,
             t->m_collections.m_session_collection_key,
             t->m_collections.m_ip_collection_key);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
-        std::string value) {
+    static void storeOrUpdateFirst(Transaction *t, const std::string &var,
+        const std::string &value) {
         t->m_collections.m_session_collection->storeOrUpdateFirst(
             var, t->m_collections.m_session_collection_key,
             t->m_rules->m_secWebAppId.m_value,
diff --git a/src/variables/time.h b/src/variables/time.h
index 60f4eb03..cdd0e652 100644
--- a/src/variables/time.h
+++ b/src/variables/time.h
@@ -31,7 +31,7 @@ namespace variables {
 
 class Time : public Variable {
  public:
-    explicit Time(std::string _name)
+    explicit Time(const std::string &_name)
         : Variable(_name),
         m_retName("TIME") { }
 
diff --git a/src/variables/time_day.h b/src/variables/time_day.h
index 9d9205b0..f444208d 100644
--- a/src/variables/time_day.h
+++ b/src/variables/time_day.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeDay : public Variable {
  public:
-    explicit TimeDay(std::string _name)
+    explicit TimeDay(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_DAY") { }
 
diff --git a/src/variables/time_epoch.h b/src/variables/time_epoch.h
index 7937d1a2..5bd6e98e 100644
--- a/src/variables/time_epoch.h
+++ b/src/variables/time_epoch.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeEpoch : public Variable {
  public:
-    explicit TimeEpoch(std::string _name)
+    explicit TimeEpoch(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_EPOCH") { }
 
diff --git a/src/variables/time_hour.h b/src/variables/time_hour.h
index 91d97bd4..8e72fdca 100644
--- a/src/variables/time_hour.h
+++ b/src/variables/time_hour.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeHour : public Variable {
  public:
-    explicit TimeHour(std::string _name)
+    explicit TimeHour(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_HOUR") { }
 
diff --git a/src/variables/time_min.h b/src/variables/time_min.h
index d608303e..b0eea95e 100644
--- a/src/variables/time_min.h
+++ b/src/variables/time_min.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeMin : public Variable {
  public:
-    explicit TimeMin(std::string _name)
+    explicit TimeMin(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_MIN") { }
 
diff --git a/src/variables/time_mon.h b/src/variables/time_mon.h
index 13f26ed0..f5694edb 100644
--- a/src/variables/time_mon.h
+++ b/src/variables/time_mon.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeMon : public Variable {
  public:
-    explicit TimeMon(std::string _name)
+    explicit TimeMon(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_MON") { }
 
diff --git a/src/variables/time_sec.h b/src/variables/time_sec.h
index 898c9732..1d6c3447 100644
--- a/src/variables/time_sec.h
+++ b/src/variables/time_sec.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeSec : public Variable {
  public:
-    explicit TimeSec(std::string _name)
+    explicit TimeSec(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_SEC") { }
 
diff --git a/src/variables/time_wday.h b/src/variables/time_wday.h
index 1ca5fc4f..dac491ea 100644
--- a/src/variables/time_wday.h
+++ b/src/variables/time_wday.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeWDay : public Variable {
  public:
-    explicit TimeWDay(std::string _name)
+    explicit TimeWDay(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_WDAY") { }
 
diff --git a/src/variables/time_year.h b/src/variables/time_year.h
index 57f9e379..1366c71c 100644
--- a/src/variables/time_year.h
+++ b/src/variables/time_year.h
@@ -30,7 +30,7 @@ namespace variables {
 
 class TimeYear : public Variable {
  public:
-    explicit TimeYear(std::string _name)
+    explicit TimeYear(const std::string &_name)
         : Variable(_name),
         m_retName("TIME_YEAR") { }
 
diff --git a/src/variables/tx.h b/src/variables/tx.h
index ac7f3005..2a72a79b 100644
--- a/src/variables/tx.h
+++ b/src/variables/tx.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class Tx_DictElement : public Variable {
  public:
-    explicit Tx_DictElement(std::string dictElement)
+    explicit Tx_DictElement(const std::string &dictElement)
         : Variable("TX:" + dictElement),
         m_dictElement("TX:" + dictElement) { }
 
@@ -65,7 +65,7 @@ class Tx_NoDictElement : public Variable {
 
 class Tx_DictElementRegexp : public VariableRegex {
  public:
-    explicit Tx_DictElementRegexp(std::string dictElement)
+    explicit Tx_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("TX", dictElement),
         m_dictElement(dictElement) { }
 
@@ -94,11 +94,11 @@ class Tx_DynamicElement : public Variable {
             m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_tx_collection->del(k);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
+    static void storeOrUpdateFirst(Transaction *t, const std::string &var,
         std::string value) {
         t->m_collections.m_tx_collection->storeOrUpdateFirst(var, value);
     }
diff --git a/src/variables/user.h b/src/variables/user.h
index b6d1a99c..38abd30c 100644
--- a/src/variables/user.h
+++ b/src/variables/user.h
@@ -34,7 +34,7 @@ namespace variables {
 
 class User_DictElement : public Variable {
  public:
-    explicit User_DictElement(std::string dictElement)
+    explicit User_DictElement(const std::string &dictElement)
         : Variable("USER:" + dictElement),
         m_dictElement("USER:" + dictElement) { }
 
@@ -67,7 +67,7 @@ class User_NoDictElement : public Variable {
 
 class User_DictElementRegexp : public VariableRegex {
  public:
-    explicit User_DictElementRegexp(std::string dictElement)
+    explicit User_DictElementRegexp(const std::string &dictElement)
         : VariableRegex("USER", dictElement),
         m_dictElement(dictElement) { }
 
@@ -99,14 +99,14 @@ class User_DynamicElement : public Variable {
             t->m_rules->m_secWebAppId.m_value, l, m_keyExclusion);
     }
 
-    void del(Transaction *t, std::string k) {
+    static void del(Transaction *t, const std::string &k) {
         t->m_collections.m_user_collection->del(k,
             t->m_collections.m_user_collection_key,
             t->m_rules->m_secWebAppId.m_value);
     }
 
-    void storeOrUpdateFirst(Transaction *t, std::string var,
-        std::string value) {
+    static void storeOrUpdateFirst(Transaction *t, const std::string &var,
+        const std::string &value) {
         t->m_collections.m_user_collection->storeOrUpdateFirst(
             var, t->m_collections.m_user_collection_key,
             t->m_rules->m_secWebAppId.m_value,
diff --git a/src/variables/variable.h b/src/variables/variable.h
index 4f6c627c..35f51003 100644
--- a/src/variables/variable.h
+++ b/src/variables/variable.h
@@ -45,7 +45,7 @@
 #define VAR_WITH_REGEX(n, N, e) \
 class n ## _DictElementRegexp : public VariableRegex { \
  public: \
-    explicit n ## _DictElementRegexp(std::string regex) \
+    explicit n ## _DictElementRegexp(const std::string &regex) \
         : VariableRegex(#N, regex) { } \
 \
     void evaluate(Transaction *transaction, \
@@ -60,7 +60,7 @@ class n ## _DictElementRegexp : public VariableRegex { \
 #define VAR_WITH_DICT_ELEMENT(n, N, e) \
 class n ## _DictElement : public VariableDictElement { \
  public: \
-    explicit n ## _DictElement(std::string dictElement) \
+    explicit n ## _DictElement(const std::string &dictElement) \
         : VariableDictElement(#N, dictElement) { } \
 \
     void evaluate(Transaction *transaction, \
@@ -114,9 +114,9 @@ class KeyExclusion {
 // FIXME: use pre built regex.
 class KeyExclusionRegex : public KeyExclusion {
  public:
-    explicit KeyExclusionRegex(Utils::Regex re)
+    explicit KeyExclusionRegex(const Utils::Regex &re)
         : m_re(re.pattern) { }
-    explicit KeyExclusionRegex(std::string re)
+    explicit KeyExclusionRegex(const std::string &re)
         : m_re(re) { }
 
     ~KeyExclusionRegex() override { }
@@ -131,7 +131,7 @@ class KeyExclusionRegex : public KeyExclusion {
 
 class KeyExclusionString : public KeyExclusion {
  public:
-    KeyExclusionString(std::string &a)
+    explicit KeyExclusionString(std::string &a)
         : m_key(utils::string::toupper(a)) { }
 
     ~KeyExclusionString() override { }
@@ -562,7 +562,7 @@ class Variable : public VariableMonkeyResolution {
     void addsKeyExclusion(Variable *v);
 
 
-    bool operator==(const Variable& b) {
+    bool operator==(const Variable& b) const {
         return m_collectionName == b.m_collectionName &&
             m_name == b.m_name &&
             *m_fullName == *b.m_fullName;
@@ -580,7 +580,7 @@ class Variable : public VariableMonkeyResolution {
 
 class VariableDictElement : public Variable {
  public:
-    VariableDictElement(std::string name, std::string dict_element)
+    VariableDictElement(const std::string &name, const std::string &dict_element)
         :  m_dictElement(dict_element), Variable(name + ":" + dict_element) { }
 
     std::string m_dictElement;
@@ -589,14 +589,14 @@ class VariableDictElement : public Variable {
 
 class VariableRegex : public Variable {
  public:
-    VariableRegex(std::string name, std::string regex)
+    VariableRegex(const std::string &name, const std::string &regex)
         :  m_r(regex),
         m_regex(regex),
         Variable(name + ":" + "regex(" + regex + ")") { }
 
+    Utils::Regex m_r;
     // FIXME: no need for that.
     std::string m_regex;
-    Utils::Regex m_r;
 };
 
 class Variables : public std::vector<Variable *> {
@@ -621,11 +621,12 @@ class Variables : public std::vector<Variable *> {
 class VariableModificatorExclusion : public Variable {
  public:
     explicit VariableModificatorExclusion(std::unique_ptr<Variable> var)
-        : m_base(std::move(var)), Variable(var.get()) { }
+        : Variable(var.get()),
+        m_base(std::move(var)) { }
 
     void evaluate(Transaction *t,
         Rule *rule,
-        std::vector<const VariableValue *> *l) {
+        std::vector<const VariableValue *> *l) override {
         m_base->evaluate(t, rule, l);
     }
 
@@ -643,7 +644,7 @@ class VariableModificatorCount : public Variable {
 
     void evaluate(Transaction *t,
         Rule *rule,
-        std::vector<const VariableValue *> *l) {
+        std::vector<const VariableValue *> *l) override {
         std::vector<const VariableValue *> reslIn;
         VariableValue *val = NULL;
         int count = 0;
diff --git a/src/variables/xml.h b/src/variables/xml.h
index eba59561..0cb4522b 100644
--- a/src/variables/xml.h
+++ b/src/variables/xml.h
@@ -55,7 +55,7 @@ class XML_NoDictElement : public Variable {
 
 class XML : public Variable {
  public:
-    explicit XML(std::string _name)
+    explicit XML(const std::string &_name)
         : Variable(_name) { }
 
     void evaluate(Transaction *transaction,