Add fixed boundary condition descriptor

src/scheme/FixedBoundaryConditionDescriptor.hpp

+#ifndef FIXED_BOUNDARY_CONDITION_DESCRIPTOR_HPP
+#define FIXED_BOUNDARY_CONDITION_DESCRIPTOR_HPP
+
+#include <language/utils/FunctionSymbolId.hpp>
+#include <scheme/IBoundaryConditionDescriptor.hpp>
+#include <scheme/IBoundaryDescriptor.hpp>
+
+#include <memory>
+
+class FixedBoundaryConditionDescriptor : public IBoundaryConditionDescriptor
+{
+ private:
+  std::ostream&
+  _write(std::ostream& os) const final
+  {
+    os << "fixed(" << m_name << ',' << *m_boundary_descriptor << ")";
+    return os;
+  }
+
+  const std::string_view m_name;
+
+  std::shared_ptr<const IBoundaryDescriptor> m_boundary_descriptor;
+
+ public:
+  std::string_view
+  name() const
+  {
+    return m_name;
+  }
+
+  const IBoundaryDescriptor&
+  boundaryDescriptor() const
+  {
+    return *m_boundary_descriptor;
+  }
+
+  Type
+  type() const final
+  {
+    return Type::fixed;
+  }
+
+  FixedBoundaryConditionDescriptor(const std::string_view name,
+                                   std::shared_ptr<const IBoundaryDescriptor> boundary_descriptor)
+    : m_name{name}, m_boundary_descriptor(boundary_descriptor)
+  {
+    ;
+  }
+
+  FixedBoundaryConditionDescriptor(const FixedBoundaryConditionDescriptor&) = delete;
+  FixedBoundaryConditionDescriptor(FixedBoundaryConditionDescriptor&&)      = delete;
+
+  ~FixedBoundaryConditionDescriptor() = default;
+};
+
+#endif   // FIXED_BOUNDARY_CONDITION_DESCRIPTOR_HPP

src/scheme/IBoundaryConditionDescriptor.hpp

@@ -10,6 +10,7 @@ class IBoundaryConditionDescriptor
   {
     dirichlet,
     fourier,
+    fixed,
     free,
     neumann,
     symmetry