diff --git a/src/df1b2-separable/df1b2chkder.cpp b/src/df1b2-separable/df1b2chkder.cpp
index b32f84781..376f4b7c1 100644
--- a/src/df1b2-separable/df1b2chkder.cpp
+++ b/src/df1b2-separable/df1b2chkder.cpp
@@ -39,7 +39,7 @@ adtimer* ad_comm::ptm1 = nullptr;
  * \param
  */
 void laplace_approximation_calculator::
-  check_derivatives(__attribute__((unused)) const dvector& _x, __attribute__((unused)) function_minimizer* pfmin, __attribute__((unused)) double f)
+  check_derivatives([[maybe_unused]] const dvector& _x, [[maybe_unused]] function_minimizer* pfmin, [[maybe_unused]] double f)
 {
 #ifdef DIAG
   cerr << "need to define this" << endl;
diff --git a/src/df1b2-separable/df1b2f15.cpp b/src/df1b2-separable/df1b2f15.cpp
index 7f1540a22..995e61366 100644
--- a/src/df1b2-separable/df1b2f15.cpp
+++ b/src/df1b2-separable/df1b2f15.cpp
@@ -23,7 +23,7 @@ void df1b2_init_vector::allocate(int mmin,int mmax,const adstring&s)
  * Description not yet available.
  * \param
  */
-void df1b2_init_vector::allocate(int mmin,int mmax,int ps, __attribute__((unused)) const adstring&s)
+void df1b2_init_vector::allocate(int mmin,int mmax,int ps, [[maybe_unused]] const adstring&s)
 {
   set_phase_start(ps);
   df1b2vector::allocate(mmin,mmax);
@@ -109,7 +109,7 @@ int initial_df1b2params::set_index(void)
  * \param
  */
 void df1b2_init_vector::set_value(const init_df1b2vector& _x,
-  const int& _ii, __attribute__((unused)) const df1b2variable& pen)
+  const int& _ii, [[maybe_unused]] const df1b2variable& pen)
 {
   ADUNCONST(init_df1b2vector,x)
   ADUNCONST(int,ii)
@@ -220,7 +220,7 @@ void df1b2_init_matrix::set_index(int aflag,const int& _ii)
  * \param
  */
 void df1b2_init_matrix::set_value(const init_df1b2vector& _x,
-  const int& _ii, __attribute__((unused)) const df1b2variable& pen)
+  const int& _ii, [[maybe_unused]] const df1b2variable& pen)
 {
   ADUNCONST(init_df1b2vector,x)
   ADUNCONST(int,ii)
@@ -245,7 +245,7 @@ void df1b2_init_matrix::set_value(const init_df1b2vector& _x,
  * \param
  */
 void df1b2_init_number::set_value(const init_df1b2vector& _x,const int& _ii,
-    __attribute__((unused)) const df1b2variable& pen)
+  [[maybe_unused]] const df1b2variable& pen)
 {
   ADUNCONST(init_df1b2vector,x)
   ADUNCONST(int,ii)
@@ -259,7 +259,7 @@ void df1b2_init_number::set_value(const init_df1b2vector& _x,const int& _ii,
  * Description not yet available.
  * \param
  */
-void df1b2_init_number::allocate(__attribute__((unused)) const adstring& s)
+void df1b2_init_number::allocate([[maybe_unused]] const adstring& s)
 {
   if (!df1b2variable::noallocate)
   {
@@ -272,7 +272,7 @@ void df1b2_init_number::allocate(__attribute__((unused)) const adstring& s)
  * Description not yet available.
  * \param
  */
-void df1b2_init_number::allocate(int _n, __attribute__((unused)) const adstring& s)
+void df1b2_init_number::allocate(int _n, [[maybe_unused]] const adstring& s)
 {
   df1b2variable::allocate();
   set_phase_start(_n);
@@ -282,7 +282,7 @@ void df1b2_init_number::allocate(int _n, __attribute__((unused)) const adstring&
  * Description not yet available.
  * \param
  */
-void df1b2variable::allocate(__attribute__((unused)) const char *s)
+void df1b2variable::allocate([[maybe_unused]] const char *s)
 {
   df1b2variable::allocate();
 }
@@ -707,7 +707,7 @@ void df1b2_init_bounded_vector::allocate(int mmin,int mmax,
  * \param
  */
 void df1b2_init_bounded_vector::allocate(int mmin,int mmax,
-  double _minb,double _maxb, __attribute__((unused)) const char* s)
+  double _minb,double _maxb, [[maybe_unused]] const char* s)
 {
   allocate(mmin,mmax,_minb,_maxb);
 }
@@ -717,7 +717,7 @@ void df1b2_init_bounded_vector::allocate(int mmin,int mmax,
  * \param
  */
 void df1b2_init_bounded_vector::allocate(int mmin,int mmax,
-  double _minb,double _maxb,int n, __attribute__((unused)) const char * s)
+  double _minb,double _maxb,int n, [[maybe_unused]] const char * s)
 {
   allocate(mmin,mmax,_minb,_maxb);
   set_phase_start(n);
diff --git a/src/df1b2-separable/df1b2f25.cpp b/src/df1b2-separable/df1b2f25.cpp
index 5d074600e..7556de3d3 100644
--- a/src/df1b2-separable/df1b2f25.cpp
+++ b/src/df1b2-separable/df1b2f25.cpp
@@ -38,7 +38,7 @@
  * Description not yet available.
  * \param
  */
-void df1b2_init_number::sd_scale(const dvector& _d, __attribute__((unused)) const dvector& x,
+void df1b2_init_number::sd_scale(const dvector& _d, [[maybe_unused]] const dvector& x,
   const int& _ii)
   {
     int& ii=(int&) _ii;
@@ -82,7 +82,7 @@ void df1b2_init_bounded_number::sd_scale(const dvector& _d,const dvector& x,
  * Description not yet available.
  * \param
  */
-void df1b2_init_vector::sd_scale(const dvector& _v, __attribute__((unused)) const dvector& x,
+void df1b2_init_vector::sd_scale(const dvector& _v, [[maybe_unused]] const dvector& x,
   const int& _ii)
   {
     if (allocated())
@@ -104,7 +104,7 @@ void df1b2_init_vector::sd_scale(const dvector& _v, __attribute__((unused)) cons
  * Description not yet available.
  * \param
  */
-void df1b2_init_matrix::sd_scale(const dvector& _v, __attribute__((unused)) const dvector& x,
+void df1b2_init_matrix::sd_scale(const dvector& _v, [[maybe_unused]] const dvector& x,
   const int& _ii)
   {
     if (allocated())
diff --git a/src/df1b2-separable/df1b2fn2.cpp b/src/df1b2-separable/df1b2fn2.cpp
index 9c2d5f0dd..47a9d82f5 100644
--- a/src/df1b2-separable/df1b2fn2.cpp
+++ b/src/df1b2-separable/df1b2fn2.cpp
@@ -804,7 +804,7 @@ double d3F(P_USER_FUNCTION pu,const init_df1b2vector& _x,int i,int j,int k,
  * Description not yet available.
  * \param
  */
-dmatrix check_second_derivatives(__attribute__((unused)) const init_df1b2vector& x)
+dmatrix check_second_derivatives([[maybe_unused]] const init_df1b2vector& x)
 {
   f1b2gradlist->set_no_derivatives();
 #ifdef OPT_LIB
@@ -831,7 +831,7 @@ dmatrix check_second_derivatives(__attribute__((unused)) const init_df1b2vector&
  * Description not yet available.
  * \param
  */
-d3_array check_third_derivatives(__attribute__((unused)) const init_df1b2vector& x)
+d3_array check_third_derivatives([[maybe_unused]] const init_df1b2vector& x)
 {
   f1b2gradlist->set_no_derivatives();
 #ifdef OPT_LIB
@@ -932,7 +932,7 @@ void re_objective_function_value::allocate(void)
  * Description not yet available.
  * \param
  */
-void re_objective_function_value::allocate(__attribute__((unused)) const char * s)
+void re_objective_function_value::allocate([[maybe_unused]] const char * s)
 {
   pobjfun=this;
   df1b2variable::allocate();
diff --git a/src/df1b2-separable/df1b2fn5.cpp b/src/df1b2-separable/df1b2fn5.cpp
index 1b3daaff4..ce573194f 100644
--- a/src/df1b2-separable/df1b2fn5.cpp
+++ b/src/df1b2-separable/df1b2fn5.cpp
@@ -103,7 +103,7 @@ df1b2variable::df1b2variable(void)
  * Description not yet available.
  * \param
  */
-df1b2variable::df1b2variable(__attribute__((unused)) const newadkludge* z)
+df1b2variable::df1b2variable([[maybe_unused]] const newadkludge* z)
 {
   ptr=0;
   ncopies=0;
@@ -154,7 +154,7 @@ void df1b2variable::allocate(void)
  * Description not yet available.
  * \param
  */
-df1b2variable::df1b2variable(__attribute__((unused)) adkludge1 * adkludgexxx)
+df1b2variable::df1b2variable([[maybe_unused]] adkludge1 * adkludgexxx)
 {
   // vectors are all 1,...,nvar
   ptr = (double*) pool->alloc();
diff --git a/src/df1b2-separable/df1b2fnl.cpp b/src/df1b2-separable/df1b2fnl.cpp
index 3500c6f72..4c08cf3ac 100644
--- a/src/df1b2-separable/df1b2fnl.cpp
+++ b/src/df1b2-separable/df1b2fnl.cpp
@@ -359,7 +359,7 @@ funnel_init_df1b2variable::funnel_init_df1b2variable
  * Description not yet available.
  * \param
  */
-void funnel_init_df1b2variable::allocate(__attribute__((unused)) const df1b2variable& x)
+void funnel_init_df1b2variable::allocate([[maybe_unused]] const df1b2variable& x)
 {
   cerr << "Haven't defined htis yet" << endl;
   ad_exit(1);
@@ -851,7 +851,7 @@ void funnel_init_df1b2vector::set_index(imatrix& y,int& ii)
  * \param
  */
 void funnel_init_df1b2vector::set_value(const init_df1b2vector& _x,
-  const int& _ii, __attribute__((unused)) const df1b2variable& _pen)
+  const int& _ii, [[maybe_unused]] const df1b2variable& _pen)
 {
   ADUNCONST(int,ii)
   ADUNCONST(init_df1b2vector,x)
@@ -942,7 +942,7 @@ void funnel_init_bounded_df1b2vector::set_index(imatrix& y,int& ii)
  * \param
  */
 void funnel_init_bounded_df1b2vector::set_value(const init_df1b2vector& _x,
-  const int& _ii, __attribute__((unused)) const df1b2variable& _pen)
+  const int& _ii, [[maybe_unused]] const df1b2variable& _pen)
 {
   ADUNCONST(int,ii)
   ADUNCONST(init_df1b2vector,x)
diff --git a/src/df1b2-separable/df1b2fun.cpp b/src/df1b2-separable/df1b2fun.cpp
index e949ae151..a1d76f638 100644
--- a/src/df1b2-separable/df1b2fun.cpp
+++ b/src/df1b2-separable/df1b2fun.cpp
@@ -574,7 +574,7 @@ double ADdiff_fun(double x,double y)
  * Description not yet available.
  * \param
  */
-double ADzero_fun(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double ADzero_fun([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return 0.0;
 }
@@ -583,7 +583,7 @@ double ADzero_fun(__attribute__((unused)) double x, __attribute__((unused)) doub
  * Description not yet available.
  * \param
  */
-double ADzero_fun(__attribute__((unused)) double x)
+double ADzero_fun([[maybe_unused]] double x)
 {
   return 0.0;
 }
@@ -592,7 +592,7 @@ double ADzero_fun(__attribute__((unused)) double x)
  * Description not yet available.
  * \param
  */
-double AD1_fun(__attribute__((unused)) double x)
+double AD1_fun([[maybe_unused]] double x)
 {
   return 1.0;
 }
@@ -601,7 +601,7 @@ double AD1_fun(__attribute__((unused)) double x)
  * Description not yet available.
  * \param
  */
-double AD1_fun(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double AD1_fun([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return 1.0;
 }
@@ -610,7 +610,7 @@ double AD1_fun(__attribute__((unused)) double x, __attribute__((unused)) double
  * Description not yet available.
  * \param
  */
-double ADm1_fun(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double ADm1_fun([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return -1.0;
 }
@@ -628,7 +628,7 @@ double AD_id(double x)
  * Description not yet available.
  * \param
  */
-double ADfirst_arg(double x, __attribute__((unused)) double y)
+double ADfirst_arg(double x, [[maybe_unused]] double y)
 {
   return x;
 }
@@ -637,7 +637,7 @@ double ADfirst_arg(double x, __attribute__((unused)) double y)
  * Description not yet available.
  * \param
  */
-double ADsecond_arg_plus1(__attribute__((unused)) double x, double y)
+double ADsecond_arg_plus1([[maybe_unused]] double x, double y)
 {
   return y+1;
 }
@@ -646,7 +646,7 @@ double ADsecond_arg_plus1(__attribute__((unused)) double x, double y)
  * Description not yet available.
  * \param
  */
-double ADsecond_arg(__attribute__((unused)) double x, double y)
+double ADsecond_arg([[maybe_unused]] double x, double y)
 {
   return y;
 }
@@ -655,7 +655,7 @@ double ADsecond_arg(__attribute__((unused)) double x, double y)
  * Description not yet available.
  * \param
  */
-double AD_div_1(__attribute__((unused)) double x, double y)
+double AD_div_1([[maybe_unused]] double x, double y)
 {
   return 1.0/y;
 }
@@ -682,7 +682,7 @@ double AD_div_22(double x,double y)
  * Description not yet available.
  * \param
  */
-double AD_div_122(__attribute__((unused)) double x, double y)
+double AD_div_122([[maybe_unused]] double x, double y)
 {
   return 2.0/(y*y*y);
 }
@@ -691,7 +691,7 @@ double AD_div_122(__attribute__((unused)) double x, double y)
  * Description not yet available.
  * \param
  */
-double AD_div_12(__attribute__((unused)) double x, double y)
+double AD_div_12([[maybe_unused]] double x, double y)
 {
   return -1.0/(y*y);
 }
@@ -700,7 +700,7 @@ double AD_div_12(__attribute__((unused)) double x, double y)
  * Description not yet available.
  * \param
  */
-double AD_div_11(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double AD_div_11([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return 0.0;
 }
@@ -709,7 +709,7 @@ double AD_div_11(__attribute__((unused)) double x, __attribute__((unused)) doubl
  * Description not yet available.
  * \param
  */
-double AD_div_111(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double AD_div_111([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return 0.0;
 }
@@ -718,7 +718,7 @@ double AD_div_111(__attribute__((unused)) double x, __attribute__((unused)) doub
  * Description not yet available.
  * \param
  */
-double AD_div_112(__attribute__((unused)) double x, __attribute__((unused)) double y)
+double AD_div_112([[maybe_unused]] double x, [[maybe_unused]] double y)
 {
   return 0.0;
 }
@@ -815,7 +815,7 @@ double ADsix_id_fun(double x)
  * Description not yet available.
  * \param
  */
-double ADsix_fun(__attribute__((unused)) double x)
+double ADsix_fun([[maybe_unused]] double x)
 {
   return 6.0;
 }
@@ -824,7 +824,7 @@ double ADsix_fun(__attribute__((unused)) double x)
  * Description not yet available.
  * \param
  */
-double ADtwo_fun(__attribute__((unused)) double x)
+double ADtwo_fun([[maybe_unused]] double x)
 {
   return 2.0;
 }
diff --git a/src/df1b2-separable/df1b2gh.cpp b/src/df1b2-separable/df1b2gh.cpp
index 58092a3f5..bb51a7086 100644
--- a/src/df1b2-separable/df1b2gh.cpp
+++ b/src/df1b2-separable/df1b2gh.cpp
@@ -22,7 +22,7 @@
  */
 double do_gauss_hermite_block_diagonal(const dvector& x,
   const dvector& u0,const dmatrix& Hess,const dvector& _xadjoint,
-  const dvector& _uadjoint, __attribute__((unused)) const dmatrix& _Hessadjoint,
+  const dvector& _uadjoint, [[maybe_unused]] const dmatrix& _Hessadjoint,
   function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
diff --git a/src/df1b2-separable/df1b2ghmult.cpp b/src/df1b2-separable/df1b2ghmult.cpp
index 43e50e278..f1e07ee2d 100644
--- a/src/df1b2-separable/df1b2ghmult.cpp
+++ b/src/df1b2-separable/df1b2ghmult.cpp
@@ -22,7 +22,7 @@
  */
 double do_gauss_hermite_block_diagonal_multi(const dvector& x,
   const dvector& u0,const dmatrix& Hess,const dvector& _xadjoint,
-  const dvector& _uadjoint, __attribute__((unused)) const dmatrix& _Hessadjoint,
+  const dvector& _uadjoint, [[maybe_unused]] const dmatrix& _Hessadjoint,
   function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
diff --git a/src/df1b2-separable/df1b2im3.cpp b/src/df1b2-separable/df1b2im3.cpp
index 91fbfa694..8fb03b2d6 100644
--- a/src/df1b2-separable/df1b2im3.cpp
+++ b/src/df1b2-separable/df1b2im3.cpp
@@ -22,7 +22,7 @@
  */
 double calculate_importance_sample_block_diagonal(const dvector& x,
   const dvector& u0,const dmatrix& Hess,const dvector& _xadjoint,
-  const dvector& _uadjoint, __attribute__((unused)) const dmatrix& _Hessadjoint,
+  const dvector& _uadjoint, [[maybe_unused]] const dmatrix& _Hessadjoint,
   function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
diff --git a/src/df1b2-separable/df1b2im3f.cpp b/src/df1b2-separable/df1b2im3f.cpp
index 16c724492..211180724 100644
--- a/src/df1b2-separable/df1b2im3f.cpp
+++ b/src/df1b2-separable/df1b2im3f.cpp
@@ -22,7 +22,7 @@
  */
 double calculate_importance_sample_block_diagonal_funnel(const dvector& x,
   const dvector& u0,const dmatrix& Hess,const dvector& _xadjoint,
-  const dvector& _uadjoint, __attribute__((unused)) const dmatrix& _Hessadjoint,
+  const dvector& _uadjoint, [[maybe_unused]] const dmatrix& _Hessadjoint,
   function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
diff --git a/src/df1b2-separable/df1b2im4.cpp b/src/df1b2-separable/df1b2im4.cpp
index a85f9e10f..17197c9e6 100644
--- a/src/df1b2-separable/df1b2im4.cpp
+++ b/src/df1b2-separable/df1b2im4.cpp
@@ -22,7 +22,7 @@
  */
 double calculate_importance_sample_block_diagonal_option2(const dvector& x,
   const dvector& u0,const dmatrix& Hess,const dvector& _xadjoint,
-  const dvector& _uadjoint, __attribute__((unused)) const dmatrix& _Hessadjoint,
+  const dvector& _uadjoint, [[maybe_unused]] const dmatrix& _Hessadjoint,
   function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
diff --git a/src/df1b2-separable/df1b2im5.cpp b/src/df1b2-separable/df1b2im5.cpp
index 06aa47106..9ca5bd9f7 100644
--- a/src/df1b2-separable/df1b2im5.cpp
+++ b/src/df1b2-separable/df1b2im5.cpp
@@ -23,7 +23,7 @@
 double calculate_importance_sample_block_diagonal_option_antithetical
   (const dvector& x,const dvector& u0,const dmatrix& Hess,
   const dvector& _xadjoint,const dvector& _uadjoint,
-  __attribute__((unused)) const dmatrix& _Hessadjoint,function_minimizer * pmin)
+  [[maybe_unused]] const dmatrix& _Hessadjoint,function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
   ADUNCONST(dvector,uadjoint)
diff --git a/src/df1b2-separable/df1b2impspf.cpp b/src/df1b2-separable/df1b2impspf.cpp
index e4cbeb076..5c33e3c67 100644
--- a/src/df1b2-separable/df1b2impspf.cpp
+++ b/src/df1b2-separable/df1b2impspf.cpp
@@ -24,7 +24,7 @@ class dvar_hs_smatrix;
  */
 double calculate_importance_sample_shess(const dvector& x,const dvector& u0,
   const dmatrix& Hess,const dvector& _xadjoint,const dvector& _uadjoint,
-  __attribute__((unused)) const dmatrix& _Hessadjoint,function_minimizer * pmin)
+  [[maybe_unused]] const dmatrix& _Hessadjoint,function_minimizer * pmin)
 {
   ADUNCONST(dvector,xadjoint)
   ADUNCONST(dvector,uadjoint)
diff --git a/src/df1b2-separable/df1b2invcumdbeta.cpp b/src/df1b2-separable/df1b2invcumdbeta.cpp
index 6ae9f096d..f91093de9 100644
--- a/src/df1b2-separable/df1b2invcumdbeta.cpp
+++ b/src/df1b2-separable/df1b2invcumdbeta.cpp
@@ -210,7 +210,7 @@
     Press, Teukolsky, Vetterling, Flannery, chapter 2
 */
   df3_three_variable betai(const df3_three_variable& a,
-    const df3_three_variable& b,const  df3_three_variable& x, __attribute__((unused)) int maxit)
+    const df3_three_variable& b,const  df3_three_variable& x, [[maybe_unused]] int maxit)
   {
     df3_three_variable bt;
 
@@ -226,7 +226,7 @@
   }
 
   df3_three_variable betai(const df3_three_variable& a,
-    const df3_three_variable& b, double x, __attribute__((unused)) int maxit)
+    const df3_three_variable& b, double x, [[maybe_unused]] int maxit)
   {
     df3_three_variable bt;
 
diff --git a/src/df1b2-separable/df1b2lap.cpp b/src/df1b2-separable/df1b2lap.cpp
index 8f0cd560d..322928a56 100644
--- a/src/df1b2-separable/df1b2lap.cpp
+++ b/src/df1b2-separable/df1b2lap.cpp
@@ -60,7 +60,7 @@ dvar_vector *
  * \param
  */
 dvector laplace_approximation_calculator::get_uhat_quasi_newton
-  (__attribute__((unused)) const dvector& x,function_minimizer * pfmin)
+  ([[maybe_unused]] const dvector& x,function_minimizer * pfmin)
 {
   std::ostream& output_stream = get_output_stream();
   //int on,nopt;
@@ -215,7 +215,7 @@ dvector laplace_approximation_calculator::get_uhat_quasi_newton
  * \param
  */
 dvector laplace_approximation_calculator::get_uhat_lm_newton
-  (__attribute__((unused)) const dvector& x,function_minimizer * pfmin)
+  ([[maybe_unused]] const dvector& x,function_minimizer * pfmin)
 {
   double f=0.0;
   //dvector g(1,usize);
@@ -324,8 +324,8 @@ laplace_approximation_calculator::laplace_approximation_calculator
 (
   int _xsize,
   int _usize,
-  __attribute__((unused)) int _minder,
-  __attribute__((unused)) int _maxder,
+  [[maybe_unused]] int _minder,
+  [[maybe_unused]] int _maxder,
   function_minimizer* _pmin
 ):
   init_switch(1),
@@ -1387,7 +1387,7 @@ void random_effects_userfunction(double f,const dvector& x, const dvector& g);
  * Description not yet available.
  * \param
  */
-void get_second_ders(__attribute__((unused)) int xs, __attribute__((unused)) int us,const init_df1b2vector _y,dmatrix& Hess,
+void get_second_ders([[maybe_unused]] int xs, [[maybe_unused]] int us,const init_df1b2vector _y,dmatrix& Hess,
   dmatrix& Dux, df1b2_gradlist * f1b2gradlist,function_minimizer * pfmin,
   laplace_approximation_calculator * lpc)
 {
@@ -1922,7 +1922,7 @@ double calculate_laplace_approximation(const dvector& x,const dvector& u0,
  * \param
  */
 void get_newton_raphson_info(int xs,int us,const init_df1b2vector _y,
-  dmatrix& Hess, dvector& grad, __attribute__((unused)) df1b2_gradlist * f1b2gradlist,
+  dmatrix& Hess, dvector& grad, [[maybe_unused]] df1b2_gradlist * f1b2gradlist,
   function_minimizer * pfmin)
 {
   // Note that xs is the number of active non random effects
@@ -1965,7 +1965,7 @@ void get_newton_raphson_info(int xs,int us,const init_df1b2vector _y,
 /**
 Does Nothing.
 */
-void laplace_approximation_calculator::check_for_need_to_reallocate(__attribute__((unused)) int ip)
+void laplace_approximation_calculator::check_for_need_to_reallocate([[maybe_unused]] int ip)
 {
 }
   //void laplace_approximation_calculator::get_newton_raphson_info
@@ -2811,7 +2811,7 @@ void nested_calls_indices::allocate(const nested_calls_shape& _nsc)
  * \param
  */
 dvector laplace_approximation_calculator::get_uhat_lm_newton2
-  (__attribute__((unused)) const dvector& x,function_minimizer * pfmin)
+  ([[maybe_unused]] const dvector& x,function_minimizer * pfmin)
 {
   std::ostream& output_stream = get_output_stream();
 
diff --git a/src/df1b2-separable/df1b2lme.cpp b/src/df1b2-separable/df1b2lme.cpp
index a938c872b..dda558711 100644
--- a/src/df1b2-separable/df1b2lme.cpp
+++ b/src/df1b2-separable/df1b2lme.cpp
@@ -125,7 +125,7 @@ void laplace_approximation_calculator::get_hessian_components_banded_lme
  * \param
  */
 dvar_matrix laplace_approximation_calculator::get_hessian_from_components_lme
-  (__attribute__((unused)) function_minimizer * pfmin)
+  ([[maybe_unused]] function_minimizer * pfmin)
 {
   int mmin=variance_components_vector->indexmin();
   int mmax=variance_components_vector->indexmax();
diff --git a/src/df1b2-separable/df1b2lp1.cpp b/src/df1b2-separable/df1b2lp1.cpp
index 2f769b26a..d7bf83775 100644
--- a/src/df1b2-separable/df1b2lp1.cpp
+++ b/src/df1b2-separable/df1b2lp1.cpp
@@ -853,7 +853,7 @@ void laplace_approximation_calculator::get_newton_raphson_info
  * Description not yet available.
  * \param
  */
-void laplace_approximation_calculator::set_u_dot(__attribute__((unused)) int ip)
+void laplace_approximation_calculator::set_u_dot([[maybe_unused]] int ip)
 {
   int mmin=y.indexmin();
   int mmax=y.indexmax();
diff --git a/src/df1b2-separable/df1b2lp11.cpp b/src/df1b2-separable/df1b2lp11.cpp
index 2b8e95cf0..de1e81671 100644
--- a/src/df1b2-separable/df1b2lp11.cpp
+++ b/src/df1b2-separable/df1b2lp11.cpp
@@ -200,8 +200,8 @@ dvector safe_choleski_solver::solve
 \todo Needs testing
 */
 void laplace_approximation_calculator::
-  do_newton_raphson_state_space(function_minimizer * pfmin, __attribute__((unused)) double f_from_1,
-  __attribute__((unused)) int& no_converge_flag)
+  do_newton_raphson_state_space(function_minimizer * pfmin, [[maybe_unused]] double f_from_1,
+  [[maybe_unused]] int& no_converge_flag)
 {
   std::ostream& output_stream = get_output_stream();
 
diff --git a/src/df1b2-separable/df1b2lp2.cpp b/src/df1b2-separable/df1b2lp2.cpp
index 87ee31a60..4e5a155b7 100644
--- a/src/df1b2-separable/df1b2lp2.cpp
+++ b/src/df1b2-separable/df1b2lp2.cpp
@@ -22,7 +22,7 @@ double calculate_laplace_approximation(const dvector& x,const dvector& u0,
   const dmatrix& Hess,const dvector& _xadjoint,const dvector& _uadjoint,
   const dmatrix& _Hessadjoint,function_minimizer * pmin);
 
-static void xxx(__attribute__((unused)) ivector re_list, __attribute__((unused)) ivector fe_list){}
+static void xxx([[maybe_unused]] ivector re_list, [[maybe_unused]] ivector fe_list){}
 
 /**
  * Description not yet available.
diff --git a/src/df1b2-separable/df1b2lp8.cpp b/src/df1b2-separable/df1b2lp8.cpp
index dac3b9f99..d6b637853 100644
--- a/src/df1b2-separable/df1b2lp8.cpp
+++ b/src/df1b2-separable/df1b2lp8.cpp
@@ -357,7 +357,7 @@ double fcomp1(dvector x,dvector d,int samplesize,int n,dvector & g,
  * Description not yet available.
  * \param
  */
-void laplace_approximation_calculator::check_hessian_type(__attribute__((unused)) const dvector& _x,
+void laplace_approximation_calculator::check_hessian_type([[maybe_unused]] const dvector& _x,
   function_minimizer * pfmin)
 {
   pfmin->pre_user_function();
diff --git a/src/df1b2-separable/df1b2lp9.cpp b/src/df1b2-separable/df1b2lp9.cpp
index ae644b157..2662a0a7a 100644
--- a/src/df1b2-separable/df1b2lp9.cpp
+++ b/src/df1b2-separable/df1b2lp9.cpp
@@ -31,7 +31,7 @@ typedef fmm* pfmm;
  * \param
  */
 dvector laplace_approximation_calculator::get_uhat_quasi_newton_block_diagonal
-  (__attribute__((unused)) const dvector& x,function_minimizer * pfmin)
+  ([[maybe_unused]] const dvector& x,function_minimizer * pfmin)
 {
   if (separable_function_difference)
   {
diff --git a/src/df1b2-separable/df1b2sumc.cpp b/src/df1b2-separable/df1b2sumc.cpp
index f036748e8..c463ee05e 100644
--- a/src/df1b2-separable/df1b2sumc.cpp
+++ b/src/df1b2-separable/df1b2sumc.cpp
@@ -38,7 +38,7 @@ void ad_read_pass2_sumc(void);
  * Description not yet available.
  * \param
  */
- int df1b2_gradlist::write_pass1_sum(__attribute__((unused)) double x,const df1b2variable * _py,
+ int df1b2_gradlist::write_pass1_sum([[maybe_unused]] double x,const df1b2variable * _py,
    df1b2variable * pz)
  {
    ADUNCONST(df1b2variable*,py)
diff --git a/src/df1b2-separable/df32fun.cpp b/src/df1b2-separable/df32fun.cpp
index 272be19b4..e6fafb38a 100644
--- a/src/df1b2-separable/df32fun.cpp
+++ b/src/df1b2-separable/df32fun.cpp
@@ -449,7 +449,7 @@ int operator >(const df3_two_variable & x, const df3_two_variable & n)
  * Description not yet available.
  * \param
  */
-void set_derivatives( df3_two_variable& z,const df3_two_variable& x, __attribute__((unused)) double u,
+void set_derivatives( df3_two_variable& z,const df3_two_variable& x, [[maybe_unused]] double u,
   double zp,double zp2,double zp3)
 {
     //*z.get_u() = u;
diff --git a/src/df1b2-separable/df33fun.cpp b/src/df1b2-separable/df33fun.cpp
index f8b6fea92..88df54940 100644
--- a/src/df1b2-separable/df33fun.cpp
+++ b/src/df1b2-separable/df33fun.cpp
@@ -487,7 +487,7 @@ df3_three_variable& df3_three_variable::operator+=(double value)
  * \param
  */
 void set_derivatives(df3_three_variable& z,const df3_three_variable& x,
-  __attribute__((unused)) double u, double zp,double zp2,double zp3)
+  [[maybe_unused]] double u, double zp,double zp2,double zp3)
 {
     //*z.get_u() = u;
 
diff --git a/src/df1b2-separable/df3gammp.cpp b/src/df1b2-separable/df3gammp.cpp
index bad9913dc..344481ae0 100644
--- a/src/df1b2-separable/df3gammp.cpp
+++ b/src/df1b2-separable/df3gammp.cpp
@@ -155,7 +155,7 @@ df3_two_variable cumd_gamma(const df3_two_variable& x,
   }
 }
 df3_two_variable cumd_exponential(const df3_two_variable& x,
-  __attribute__((unused)) const df3_two_variable& a)
+  [[maybe_unused]] const df3_two_variable& a)
 {
   df3_two_variable tmp;
   if (value(x)<=0)
diff --git a/src/df1b2-separable/f1b23d1.cpp b/src/df1b2-separable/f1b23d1.cpp
index 50cfb1dca..5c62dc964 100644
--- a/src/df1b2-separable/f1b23d1.cpp
+++ b/src/df1b2-separable/f1b23d1.cpp
@@ -73,7 +73,7 @@ df1b23array::df1b23array(void)
  * \param
  */
 void df1b23array::allocate(int nrl,int nrh,int ncl,int nch,
-  int nxl,int nxh, __attribute__((unused)) const char * s)
+  int nxl,int nxh, [[maybe_unused]] const char * s)
 {
   allocate(nrl,nrh,ncl,nch,nxl,nxh);
 }
@@ -98,7 +98,7 @@ void df1b23array::allocate(int nrl,int nrh,const index_type& ncl,
 void df1b23array::allocate(int nrl,int nrh,
   const index_type& ncl, const index_type& nch,
   const index_type& nxl, const index_type& nxh,
-  __attribute__((unused)) const char * s)
+  [[maybe_unused]] const char * s)
 {
   allocate(nrl,nrh,ncl,nch,nxl,nxh);
 }
@@ -222,7 +222,7 @@ void df1b23array::allocate(
   const int nrl, const int nrh,
   const ivector& ncl, const ivector& nch,
   const int nxl, const int nxh,
-  __attribute__((unused)) const char* s)
+  [[maybe_unused]] const char* s)
 {
   index_min=nrl;
   index_max=nrh;
diff --git a/src/df1b2-separable/f1b2fnl6.cpp b/src/df1b2-separable/f1b2fnl6.cpp
index 6e10def30..f655b2ac0 100644
--- a/src/df1b2-separable/f1b2fnl6.cpp
+++ b/src/df1b2-separable/f1b2fnl6.cpp
@@ -142,7 +142,7 @@ void funnel_init_df1b2matrix::set_index(imatrix& y,int& ii)
  * \param
  */
 void funnel_init_df1b2matrix::set_value(const init_df1b2vector& _x,
-  const int& _ii, __attribute__((unused)) const df1b2variable& _pen)
+  const int& _ii, [[maybe_unused]] const df1b2variable& _pen)
 {
   ADUNCONST(int,ii)
   ADUNCONST(init_df1b2vector,x)
diff --git a/src/df1b2-separable/f1b2lapqd.cpp b/src/df1b2-separable/f1b2lapqd.cpp
index 7dac823cf..2c37f331a 100644
--- a/src/df1b2-separable/f1b2lapqd.cpp
+++ b/src/df1b2-separable/f1b2lapqd.cpp
@@ -25,7 +25,7 @@ double calculate_laplace_approximation(const dvector& x,const dvector& u0,
  * \param
  */
 dvector laplace_approximation_calculator::get_uhat_quasi_newton_qd
-  (__attribute__((unused)) const dvector& x, __attribute__((unused)) function_minimizer * pfmin)
+  ([[maybe_unused]] const dvector& x, [[maybe_unused]] function_minimizer * pfmin)
 {
   dvector g(1,usize);
   independent_variables u(1,usize);
diff --git a/src/df1b2-separable/f1b2lndt.cpp b/src/df1b2-separable/f1b2lndt.cpp
index 7ae9c734e..b3d35ad85 100644
--- a/src/df1b2-separable/f1b2lndt.cpp
+++ b/src/df1b2-separable/f1b2lndt.cpp
@@ -152,7 +152,7 @@ df1b2matrix_pair::df1b2matrix_pair(const df1b2matrix& _a,
   const df1b2matrix& _b) : a(_a), b(_b)
 {}
 
-void ludcmp(const df1b2matrix& M, __attribute__((unused)) int kludge)
+void ludcmp(const df1b2matrix& M, [[maybe_unused]] int kludge)
 {
   // do lu decomp once to get ordering
   int mmin=M.indexmin();
@@ -296,7 +296,7 @@ df1b2matrix_pair ludcmp(const df1b2matrix& a)
 dmatrix reorder(const dmatrix& CM,ivector & indx);
 ivector getreindex(ivector & indx);
 
-df1b2variable ln_det(const df1b2matrix& M, __attribute__((unused)) int & sgn)
+df1b2variable ln_det(const df1b2matrix& M, [[maybe_unused]] int & sgn)
 {
   int mmin=M.indexmin();
   int mmax=M.indexmax();
@@ -405,7 +405,7 @@ df1b2vector solve(df1b2matrix& M,df1b2vector& v,const df1b2variable& _ln_det)
 }
 
 df1b2vector solve(df1b2matrix& M,df1b2vector& v,const df1b2variable& _ln_det,
-  __attribute__((unused)) const int& sgn)
+  [[maybe_unused]] const int& sgn)
 {
   df1b2variable& ln_det = (df1b2variable&) _ln_det;
   int mmin=M.indexmin();
diff --git a/src/df1b2-separable/f1b2sol2.cpp b/src/df1b2-separable/f1b2sol2.cpp
index 0e1cdc43b..5eb974b90 100644
--- a/src/df1b2-separable/f1b2sol2.cpp
+++ b/src/df1b2-separable/f1b2sol2.cpp
@@ -25,7 +25,7 @@ df1b2vector solve(const df1b2matrix& aa,const df1b2vector& z,
   const df1b2variable & ln_unsigned_det,double& sign);
 
 df1b2vector solve(const df1b2matrix& aa,const df1b2vector& z,
-  const df1b2variable& ld, __attribute__((unused)) df1b2variable& sign)
+  const df1b2variable& ld, [[maybe_unused]] df1b2variable& sign)
 {
   double sgn = 0;
   return solve(aa,z,ld,sgn);
diff --git a/src/df1b2-separable/f1b2trst.cpp b/src/df1b2-separable/f1b2trst.cpp
index af12ce9e6..3694756cb 100644
--- a/src/df1b2-separable/f1b2trst.cpp
+++ b/src/df1b2-separable/f1b2trst.cpp
@@ -17,7 +17,7 @@
  * Description not yet available.
  * \param
  */
-void function_minimizer::trust_region_update(int nvar, __attribute__((unused)) int _crit,
+void function_minimizer::trust_region_update(int nvar, [[maybe_unused]] int _crit,
   independent_variables& x,const dvector& _g,const double& _f)
 {
   double & f= (double&)_f;
diff --git a/src/df1b2-separable/f1b2vc1.cpp b/src/df1b2-separable/f1b2vc1.cpp
index d41092dcd..0bd68bbfd 100644
--- a/src/df1b2-separable/f1b2vc1.cpp
+++ b/src/df1b2-separable/f1b2vc1.cpp
@@ -636,7 +636,7 @@ void df1b2vector::allocate(void)
  * Description not yet available.
  * \param
  */
-void df1b2vector::allocate(int lb,int ub, __attribute__((unused)) const char * s)
+void df1b2vector::allocate(int lb,int ub, [[maybe_unused]] const char * s)
 {
   allocate(lb,ub);
 }
@@ -830,7 +830,7 @@ df1b2vector::df1b2vector(const predf1b2vector& pdv)
  * Description not yet available.
  * \param
  */
- void ADMB_getcallindex(__attribute__((unused)) const df1b2variable& x)
+ void ADMB_getcallindex([[maybe_unused]] const df1b2variable& x)
  {
    cout << "HERE" << endl;
  }
@@ -839,7 +839,7 @@ df1b2vector::df1b2vector(const predf1b2vector& pdv)
  * Description not yet available.
  * \param
  */
- void ADMB_getcallindex(__attribute__((unused)) const df1b2vector& x)
+ void ADMB_getcallindex([[maybe_unused]] const df1b2vector& x)
  {
    cout << "HERE" << endl;
  }
@@ -848,7 +848,7 @@ df1b2vector::df1b2vector(const predf1b2vector& pdv)
  * Description not yet available.
  * \param
  */
- void ADMB_getcallindex(__attribute__((unused)) const df1b2matrix& x)
+ void ADMB_getcallindex([[maybe_unused]] const df1b2matrix& x)
  {
    cout << "HERE" << endl;
  }
diff --git a/src/df1b2-separable/f1b2vc5.cpp b/src/df1b2-separable/f1b2vc5.cpp
index a0143d6ee..ddc875915 100644
--- a/src/df1b2-separable/f1b2vc5.cpp
+++ b/src/df1b2-separable/f1b2vc5.cpp
@@ -641,7 +641,7 @@ df1b2matrix::df1b2matrix(void)
  * Description not yet available.
  * \param
  */
-void df1b2matrix::allocate(int nrl,int nrh,int ncl,int nch, __attribute__((unused)) const char * s)
+void df1b2matrix::allocate(int nrl,int nrh,int ncl,int nch, [[maybe_unused]] const char * s)
 {
   allocate(nrl,nrh,ncl,nch);
 }
@@ -651,7 +651,7 @@ void df1b2matrix::allocate(int nrl,int nrh,int ncl,int nch, __attribute__((unuse
  * \param
  */
 void df1b2matrix::allocate(int nrl,int nrh,const index_type& ncl,
-  const index_type& nch, __attribute__((unused)) const char * s)
+  const index_type& nch, [[maybe_unused]] const char * s)
 {
   allocate(nrl,nrh,ncl,nch);
 }
diff --git a/src/df1b2-separable/fquadpri.cpp b/src/df1b2-separable/fquadpri.cpp
index 54d14d1b6..fe7124d89 100644
--- a/src/df1b2-separable/fquadpri.cpp
+++ b/src/df1b2-separable/fquadpri.cpp
@@ -127,12 +127,12 @@ df1b2quadratic_prior::~df1b2quadratic_prior(void)
 }
 
 void df1b2quadratic_prior::allocate(const df1b2_init_vector& _u,
-  __attribute__((unused)) const char* s)
+  [[maybe_unused]] const char* s)
   {
     allocate(_u);
   }
   void df1b2quadratic_prior::allocate(const df1b2matrix & _M,
-    const df1b2_init_vector & _u, __attribute__((unused)) const char * s)
+    const df1b2_init_vector & _u, [[maybe_unused]] const char * s)
   {
     allocate(_M,_u);
   }
@@ -316,11 +316,11 @@ void constant_df1b2quadratic_re_penalty::set_old_style_flag(void)
 {
   old_style_flag=2;
 }
-void constant_df1b2quadratic_re_penalty::operator = (__attribute__((unused)) const dmatrix & M)
+void constant_df1b2quadratic_re_penalty::operator = ([[maybe_unused]] const dmatrix & M)
 {
   //df1b2quadratic_prior::operator = (M);
 }
-void df1b2quadratic_prior::operator = (__attribute__((unused)) const dmatrix & M)
+void df1b2quadratic_prior::operator = ([[maybe_unused]] const dmatrix & M)
 {
   quadratic_prior::in_qp_calculations=0;
   num_active_parameters=funnel_init_var::num_vars;
diff --git a/src/df1b2-separable/quadpri.cpp b/src/df1b2-separable/quadpri.cpp
index c8a815443..b75a4f495 100644
--- a/src/df1b2-separable/quadpri.cpp
+++ b/src/df1b2-separable/quadpri.cpp
@@ -496,7 +496,7 @@ quadratic_prior::~quadratic_prior()
  * Description not yet available.
  * \param
  */
-  void quadratic_prior::allocate( const dvar_vector & _u, __attribute__((unused)) const char * s)
+  void quadratic_prior::allocate( const dvar_vector & _u, [[maybe_unused]] const char * s)
   {
     allocate(_u);
   }
@@ -521,7 +521,7 @@ quadratic_prior::~quadratic_prior()
  * \param
  */
   void quadratic_prior::allocate(const dvar_matrix & _M,
-    const dvar_vector & _u, __attribute__((unused)) const char * s)
+    const dvar_vector & _u, [[maybe_unused]] const char * s)
   {
     allocate(_M,_u);
   }