[mcmc/base_adapter][NFC] add const and noexcept where appropriate

allow querying the `adapting()` status of a const sampler, and
mark loading/storing the bool member noexcept, after checking the relevant
overrides in the derived `adapt_...` samplers.

Author: kedartal

src/stan/mcmc/base_adapter.hpp

@@ -6,13 +6,13 @@ namespace mcmc {
 
 class base_adapter {
  public:
-  base_adapter() : adapt_flag_(false) {}
+  base_adapter() noexcept : adapt_flag_(false) {}
 
-  virtual void engage_adaptation() { adapt_flag_ = true; }
+  virtual void engage_adaptation() noexcept { adapt_flag_ = true; }
 
-  virtual void disengage_adaptation() { adapt_flag_ = false; }
+  virtual void disengage_adaptation() noexcept { adapt_flag_ = false; }
 
-  bool adapting() { return adapt_flag_; }
+  bool adapting() const noexcept { return adapt_flag_; }
 
  protected:
   bool adapt_flag_;

src/stan/mcmc/hmc/nuts/adapt_dense_e_nuts.hpp

@@ -42,7 +42,7 @@ class adapt_dense_e_nuts : public dense_e_nuts<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts/adapt_diag_e_nuts.hpp

@@ -42,7 +42,7 @@ class adapt_diag_e_nuts : public diag_e_nuts<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts/adapt_softabs_nuts.hpp

@@ -31,7 +31,7 @@ class adapt_softabs_nuts : public softabs_nuts<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts/adapt_unit_e_nuts.hpp

@@ -31,7 +31,7 @@ class adapt_unit_e_nuts : public unit_e_nuts<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts_classic/adapt_dense_e_nuts_classic.hpp

@@ -42,7 +42,7 @@ class adapt_dense_e_nuts_classic : public dense_e_nuts_classic<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts_classic/adapt_diag_e_nuts_classic.hpp

@@ -43,7 +43,7 @@ class adapt_diag_e_nuts_classic : public diag_e_nuts_classic<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/nuts_classic/adapt_unit_e_nuts_classic.hpp

@@ -32,7 +32,7 @@ class adapt_unit_e_nuts_classic : public unit_e_nuts_classic<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/static/adapt_dense_e_static_hmc.hpp

@@ -46,7 +46,7 @@ class adapt_dense_e_static_hmc : public dense_e_static_hmc<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }

src/stan/mcmc/hmc/static/adapt_diag_e_static_hmc.hpp

@@ -46,7 +46,7 @@ class adapt_diag_e_static_hmc : public diag_e_static_hmc<Model, BaseRNG>,
     return s;
   }
 
-  void disengage_adaptation() {
+  void disengage_adaptation() noexcept {
     base_adapter::disengage_adaptation();
     this->stepsize_adaptation_.complete_adaptation(this->nom_epsilon_);
   }