Attempting Mac build fix

multibody/topology/link_joint_graph.h

@@ -266,19 +266,16 @@ class LinkJointGraph {
   }
 
   const std::vector<Link>& links() const { return data_.links; }
-  const Link& links(LinkIndex link_index) const {
-    return links().at(link_index);
-  }
+  inline const Link& links(LinkIndex link_index) const;  // Defined below.
+
   const std::vector<Joint>& joints() const { return data_.joints; }
-  const Joint& joints(JointIndex joint_index) const {
-    return joints().at(joint_index);
-  }
+  inline const Joint& joints(JointIndex joint_index) const;  // Defined below.
+
   const std::vector<Constraint>& constraints() const {
     return data_.constraints;
   }
-  const Constraint& constraints(ConstraintIndex constraint_index) const {
-    return constraints().at(constraint_index);
-  }
+  // Defined below.
+  inline const Constraint& constraints(ConstraintIndex constraint_index) const;
 
   /** Links with this index or higher were added during modeling. */
   int num_user_links() const { return data_.num_user_links; }
@@ -408,11 +405,9 @@ class LinkJointGraph {
  private:
   friend class SpanningForest;
 
-  Link& mutable_link(LinkIndex link_index) { return data_.links[link_index]; }
+  inline Link& mutable_link(LinkIndex link_index);  // Defined below.
 
-  Joint& mutable_joint(JointIndex joint_index) {
-    return data_.joints[joint_index];
-  }
+  inline Joint& mutable_joint(JointIndex joint_index);  // Defined below.
 
   // For use by SpanningForest.
   void set_primary_mobod_for_link(LinkIndex link_index,
@@ -737,6 +732,12 @@ class LinkJointGraph::Link {
   CompositeLinkIndex composite_link_index_;  // Invalid if not in composite.
 };
 
+// Definitions deferred until Link available.
+
+inline auto LinkJointGraph::links(LinkIndex link_index) const -> const Link& {
+  return links().at(link_index);
+}
+
 inline MobodIndex LinkJointGraph::link_to_mobod(LinkIndex index) const {
   return links(index).mobod_;
 }
@@ -763,6 +764,10 @@ inline bool LinkJointGraph::must_treat_as_massless(LinkIndex link_index) const {
   return link.treat_as_massless();
 }
 
+inline auto LinkJointGraph::mutable_link(LinkIndex link_index) -> Link& {
+  return data_.links[link_index];
+}
+
 /* Overloads to make JointFlags behave in a civilized manner. */
 inline JointFlags operator|(JointFlags left, JointFlags right) {
   return static_cast<JointFlags>(static_cast<unsigned>(left) |
@@ -887,6 +892,13 @@ class LinkJointGraph::Joint {
       how_modeled_;
 };
 
+// Definitions deferred until Joint available.
+
+inline auto LinkJointGraph::joints(JointIndex joint_index) const
+    -> const Joint& {
+  return joints().at(joint_index);
+}
+
 inline void LinkJointGraph::set_mobod_for_joint(JointIndex joint_index,
                                                 MobodIndex mobod_index) {
   Joint& joint = mutable_joint(joint_index);
@@ -906,6 +918,10 @@ inline void LinkJointGraph::change_joint_flags(JointIndex joint_index,
   mutable_joint(joint_index).set_flags(flags);
 }
 
+inline auto LinkJointGraph::mutable_joint(JointIndex joint_index) -> Joint& {
+  return data_.joints[joint_index];
+}
+
 /** A constraint that restricts the relative motion of two Links. The
 parent/child distinction sets the sign convention for the constraint
 multipliers. Added welds between a primary %Link and one of its shadow Links
@@ -942,6 +958,13 @@ class LinkJointGraph::Constraint {
   LinkIndex child_link_index_;
 };
 
+// Definitions deferred until Constraint availble.
+
+inline auto LinkJointGraph::constraints(ConstraintIndex constraint_index) const
+    -> const Constraint& {
+  return constraints().at(constraint_index);
+}
+
 struct LinkJointGraph::JointType {
   std::string type_name;
   int nq{-1};

multibody/topology/spanning_forest.h

@@ -179,19 +179,17 @@ class SpanningForest {
   const std::vector<Mobod>& mobods() const { return data_.mobods; }
   /** Provides convenient access to a particular Mobod.
   @pre mobod_index is in range */
-  const Mobod& mobods(MobodIndex mobod_index) const {
-    return mobods()[mobod_index];
-  }
+  inline const Mobod& mobods(MobodIndex mobod_index) const;  // Defined below.
+
   /** The mobilized body (Mobod) corresponding to the World Link. */
   const Mobod& world_mobod() const { return mobods(MobodIndex(0)); }
 
   /** Constraints we added to close loops we had to cut. */
   const std::vector<LoopConstraint>& loop_constraints() const {
     return data_.loop_constraints;
   }
-  const LoopConstraint& loop_constraints(LoopConstraintIndex index) const {
-    return loop_constraints()[index];
-  }
+  inline const LoopConstraint& loop_constraints(  // Defined below.
+      LoopConstraintIndex index) const;
 
   /** The partitioning of the forest of mobilized bodies into trees. Each Tree
   has a base (root) mobilized body that is connected directly to the World
@@ -200,7 +198,7 @@ class SpanningForest {
   const std::vector<Tree>& trees() const { return data_.trees; }
   /** Provides convenient access to a particular Tree.
   @pre tree_index is in range */
-  const Tree& trees(TreeIndex tree_index) const { return trees()[tree_index]; }
+  inline const Tree& trees(TreeIndex tree_index) const;  // Defined below.
 
   /** Returns the height of the Forest, defined as the height of the tallest
   Tree in the Forest, plus 1 for World. This is always at least 1 since World
@@ -248,13 +246,14 @@ class SpanningForest {
   Mobod represents a Composite of many Links, the Link returned here is the
   "representative" Link, that is, the one whose mobilizer is used for the whole
   Composite. Cost is O(1) and very fast. */
-  inline LinkIndex mobod_to_link(MobodIndex mobod_index) const;  // see below
+  // Defined below.
+  inline LinkIndex mobod_to_link(MobodIndex mobod_index) const;
 
   /** Returns all the Links mobilized by this Mobod. The "representative"
   Link returned by mobod_to_link() comes first, then any other Links in the
   same Composite. */
   inline const std::vector<LinkIndex>& mobod_to_links(
-      MobodIndex mobod_index) const;  // see below
+      MobodIndex mobod_index) const;  // Defined below.
 
   /** Returns the total number of generalized position coordinates q used by
   this model. O(1), very fast. */
@@ -609,6 +608,13 @@ class SpanningForest::Mobod {
   int nv_{-1};  // within the full v vector
 };
 
+// Definitions deferred until Mobod available.
+
+inline auto SpanningForest::mobods(MobodIndex mobod_index) const
+    -> const Mobod& {
+  return mobods()[mobod_index];
+}
+
 //============================= Loop Constraint ================================
 /** Weld constraints added during modeling to close loops. */
 class SpanningForest::LoopConstraint {
@@ -636,6 +642,13 @@ class SpanningForest::LoopConstraint {
   ConstraintIndex graph_constraint_index_;  // As added to the graph.
 };
 
+// Definitions deferred until LoopConstraint available.
+
+inline auto SpanningForest::loop_constraints(LoopConstraintIndex index) const
+    -> const LoopConstraint& {
+  return loop_constraints()[index];
+}
+
 //================================== Tree ======================================
 /** Everything you might want to know about an individual tree in the forest.
 A Tree consists of consecutively numbered Mobod nodes in depth first order.
@@ -703,6 +716,12 @@ class SpanningForest::Tree {
   const SpanningForest* forest_{nullptr};  // The containing forest.
 };
 
+// Definitions deferred until Tree available.
+
+inline auto SpanningForest::trees(TreeIndex tree_index) const -> const Tree& {
+  return trees()[tree_index];
+}
+
 //================================ inlines =====================================
 
 inline LinkIndex SpanningForest::mobod_to_link(MobodIndex mobod_index) const {