add a new overload of the getVariableOffset function

Author: thelfer

include/MGIS/Behaviour/Variable.hxx

@@ -119,6 +119,19 @@ namespace mgis::behaviour {
    */
   MGIS_EXPORT [[nodiscard]] size_type getVariableOffset(
       const std::vector<Variable> &, const std::string_view, const Hypothesis);
+  /*!
+   * \return the offset of the given variable for the given hypothesis
+   *
+   * \param[in] ctx: execution context
+   * \param[in] vs: variables
+   * \param[in] n: variable name
+   * \param[in] h: modelling hypothesis
+   */
+  MGIS_EXPORT [[nodiscard]] std::optional<size_type> getVariableOffset(
+      Context &,
+      const std::vector<Variable> &,
+      const std::string_view,
+      const Hypothesis) noexcept;
   /*!
    * \return the type of the given variable as a string
    * \param[in] v: variable

src/Variable.cxx

@@ -364,6 +364,21 @@ namespace mgis::behaviour {
     raise("getVariableOffset: no variable named '" + std::string(n) + "'");
   }  // end of getVariableOffset
 
+  std::optional<size_type> getVariableOffset(Context &ctx,
+                                             const std::vector<Variable> &vs,
+                                             const std::string_view n,
+                                             const Hypothesis h) noexcept {
+    auto o = size_type{};
+    for (const auto &v : vs) {
+      if (v.name == n) {
+        return o;
+      }
+      o += getVariableSize(v, h);
+    }
+    return ctx.registerErrorMessage("getVariableOffset: no variable named '" +
+                                    std::string(n) + "'");
+  }  // end of getVariableOffset
+
   std::string getVariableTypeSymbolicRepresentation(const int id) {
     auto t = id;
     const auto s = internals::getVariableTypeSymbolicRepresentation(t);