Rename Fn to FnRef, FnMut to FnMutRef and FnOnce to FnOnceRef

These are concrete impls of what will be the Fn/FnMut/FnOnce concepts
that are a light reference around the thing they call while erasing its
type to avoid requiring a template to receive and use a callable thing
in a function (that doesn't store the callable).

They are however not constexpr due to language limitations so in
constexpr vocab types, the concepts will need to be used directly.

Author: danakj

subdoc/lib/database.h

@@ -146,7 +146,7 @@ struct FunctionElement : public CommentElement {
       return sus::none();
   }
 
-  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) { fn(comment); }
+  void for_each_comment(sus::fn::FnMutRef<void(Comment&)> fn) { fn(comment); }
 };
 
 struct FieldElement : public CommentElement {
@@ -187,7 +187,7 @@ struct FieldElement : public CommentElement {
       return sus::none();
   }
 
-  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) { fn(comment); }
+  void for_each_comment(sus::fn::FnMutRef<void(Comment&)> fn) { fn(comment); }
 };
 
 struct NamespaceId {
@@ -324,7 +324,7 @@ struct RecordElement : public TypeElement {
     return out;
   }
 
-  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) {
+  void for_each_comment(sus::fn::FnMutRef<void(Comment&)> fn) {
     fn(comment);
     for (auto& [k, e] : records) e.for_each_comment(fn);
     for (auto& [k, e] : fields) e.for_each_comment(fn);
@@ -427,7 +427,7 @@ struct NamespaceElement : public CommentElement {
     return out;
   }
 
-  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) {
+  void for_each_comment(sus::fn::FnMutRef<void(Comment&)> fn) {
     fn(comment);
     for (auto& [k, e] : namespaces) e.for_each_comment(fn);
     for (auto& [k, e] : records) e.for_each_comment(fn);

subspace/CMakeLists.txt

@@ -51,7 +51,7 @@ target_sources(subspace PUBLIC
     "fn/bind.h"
     "fn/fn_box_defn.h"
     "fn/fn_box_impl.h"
-    "fn/fn_defn.h"
+    "fn/fn_ref.h"
     "iter/__private/into_iterator_archetype.h"
     "iter/__private/iterator_end.h"
     "iter/__private/iterator_loop.h"
@@ -153,7 +153,7 @@ add_executable(subspace_unittests
     "construct/into_unittest.cc"
     "construct/default_unittest.cc"
     "fn/fn_box_unittest.cc"
-    "fn/fn_unittest.cc"
+    "fn/fn_ref_unittest.cc"
     "iter/iterator_unittest.cc"
     "mem/addressof_unittest.cc"
     "mem/clone_unittest.cc"

subspace/fn/bind.h

@@ -27,7 +27,7 @@
 #include "subspace/mem/move.h"
 
 /// Bind a const lambda to storage for its bound arguments. The output can be
-/// used to construct a FnOnce, FnMut, or Fn.
+/// used to construct a FnOnceBox, FnMutBox, or FnBox.
 ///
 /// The first argument is a list of variables that will be bound into storage
 /// for access from the lambda, wrapped in sus_store(). If there are no
@@ -79,8 +79,8 @@
   }()
 
 /// A variant of `sus_bind()` which only takes a lambda, omitting the
-/// `sus_store()` list.  The output can be used to construct a FnOnce, FnMut, or
-/// Fn.
+/// `sus_store()` list.  The output can be used to construct a FnOnceBox,
+/// FnMutBox, or FnBox.
 ///
 /// Because there is no `sus_store()` list, the lambda can not capture variables
 /// from the outside scope, however it can still declare captures contained
@@ -89,15 +89,15 @@
 /// # Example
 ///
 /// This defines a lambda with a capture `a` of type `int`, and binds it so it
-/// can be used to construct a FnOnce, FnMut, or Fn.
+/// can be used to construct a FnOnceBox, FnMutBox, or FnBox.
 /// ```
 /// sus_bind0([a = int(1)](char, int){})
 /// ```
 #define sus_bind0(lambda, ...) \
   sus_bind(sus_store(), lambda __VA_OPT__(, ) __VA_ARGS__)
 
 /// Bind a mutable lambda to storage for its bound arguments. The output can be
-/// used to construct a FnOnce or FnMut.
+/// used to construct a FnOnceBox or FnMutBox.
 ///
 /// Because the storage is mutable, the lambda may capture references to the
 /// storage and mutate it, and the lambda itself may be marked mutable.
@@ -144,7 +144,8 @@
   }()
 
 /// A variant of `sus_bind_mut()` which only takes a lambda, omitting the
-/// `sus_store()` list.  The output can be used to construct a FnOnce or FnMut.
+/// `sus_store()` list.  The output can be used to construct a FnOnceBox or
+/// FnMutBox.
 ///
 /// Because there is no `sus_store()` list, the lambda can not capture variables
 /// from the outside scope, however it can still declare captures contained
@@ -155,7 +156,7 @@
 /// # Example
 ///
 /// This defines a lambda with a capture `a` of type `int`, and binds it so it
-/// can be used to construct a FnOnce, FnMut, or Fn.
+/// can be used to construct a FnOnceBox, FnMutBox, or FnBox.
 /// ```
 /// sus_bind0_mut([a = int(1)](char, int){})
 /// ```

subspace/fn/fn.h

@@ -17,4 +17,4 @@
 #include "subspace/fn/bind.h"
 #include "subspace/fn/fn_box_defn.h"
 #include "subspace/fn/fn_box_impl.h"
-#include "subspace/fn/fn_defn.h"
+#include "subspace/fn/fn_ref.h"