Replace BoxFn with Fn when it's not an lvalue

Author: danakj

subdoc/lib/database.h

@@ -25,6 +25,7 @@
 #include "subdoc/lib/unique_symbol.h"
 #include "subdoc/llvm.h"
 #include "subspace/choice/choice.h"
+#include "subspace/fn/fn.h"
 #include "subspace/option/option.h"
 #include "subspace/prelude.h"
 
@@ -145,7 +146,7 @@ struct FunctionElement : public CommentElement {
       return sus::none();
   }
 
-  void for_each_comment(sus::fn::BoxFnMut<void(Comment&)>& fn) { fn(comment); }
+  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) { fn(comment); }
 };
 
 struct FieldElement : public CommentElement {
@@ -186,7 +187,7 @@ struct FieldElement : public CommentElement {
       return sus::none();
   }
 
-  void for_each_comment(sus::fn::BoxFnMut<void(Comment&)>& fn) { fn(comment); }
+  void for_each_comment(sus::fn::FnMut<void(Comment&)> fn) { fn(comment); }
 };
 
 struct NamespaceId {
@@ -323,7 +324,7 @@ struct RecordElement : public TypeElement {
     return out;
   }
 
-  void for_each_comment(sus::fn::BoxFnMut<void(Comment&)>& fn) {
+  void for_each_comment(sus::fn::FnMut<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);
@@ -426,7 +427,7 @@ struct NamespaceElement : public CommentElement {
     return out;
   }
 
-  void for_each_comment(sus::fn::BoxFnMut<void(Comment&)>& fn) {
+  void for_each_comment(sus::fn::FnMut<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/fn/box_fn_defn.h

@@ -186,7 +186,7 @@ class [[sus_trivial_abi]] BoxFnOnce<R(CallArgs...)> {
   BoxFnOnce& operator=(const BoxFnOnce&) noexcept = delete;
 
   /// Runs and consumes the closure.
-  inline R operator()(CallArgs&&... args) && noexcept;
+  inline R operator()(CallArgs... args) && noexcept;
 
   /// `sus::construct::From` trait implementation.
   //
@@ -339,8 +339,8 @@ class [[sus_trivial_abi]] BoxFnMut<R(CallArgs...)>
   BoxFnMut& operator=(const BoxFnMut&) noexcept = delete;
 
   /// Runs the closure.
-  inline R operator()(CallArgs&&... args) & noexcept;
-  inline R operator()(CallArgs&&... args) && noexcept {
+  inline R operator()(CallArgs... args) & noexcept;
+  inline R operator()(CallArgs... args) && noexcept {
     return static_cast<BoxFnOnce<R(CallArgs...)>&&>(*this)(
         forward<CallArgs>(args)...);
   }
@@ -471,8 +471,8 @@ class [[sus_trivial_abi]] BoxFn<R(CallArgs...)> final
   BoxFn& operator=(const BoxFn&) noexcept = delete;
 
   /// Runs the closure.
-  inline R operator()(CallArgs&&... args) const& noexcept;
-  inline R operator()(CallArgs&&... args) && noexcept {
+  inline R operator()(CallArgs... args) const& noexcept;
+  inline R operator()(CallArgs... args) && noexcept {
     return static_cast<BoxFnOnce<R(CallArgs...)>&&>(*this)(
         forward<CallArgs>(args)...);
   }

subspace/fn/box_fn_impl.h

@@ -130,7 +130,7 @@ BoxFnOnce<R(CallArgs...)>& BoxFnOnce<R(CallArgs...)>::operator=(BoxFnOnce&& o) n
 }
 
 template <class R, class... CallArgs>
-R BoxFnOnce<R(CallArgs...)>::operator()(CallArgs&&... args) && noexcept {
+R BoxFnOnce<R(CallArgs...)>::operator()(CallArgs... args) && noexcept {
   switch (type_) {
     case __private::BoxFnPointer: {
       ::sus::check(fn_ptr_);  // Catch use-after-move.
@@ -163,7 +163,7 @@ R BoxFnOnce<R(CallArgs...)>::operator()(CallArgs&&... args) && noexcept {
 }
 
 template <class R, class... CallArgs>
-R BoxFnMut<R(CallArgs...)>::operator()(CallArgs&&... args) & noexcept {
+R BoxFnMut<R(CallArgs...)>::operator()(CallArgs... args) & noexcept {
   using Super = BoxFnOnce<R(CallArgs...)>;
   switch (Super::type_) {
     case __private::BoxFnPointer:
@@ -183,7 +183,7 @@ R BoxFnMut<R(CallArgs...)>::operator()(CallArgs&&... args) & noexcept {
 }
 
 template <class R, class... CallArgs>
-R BoxFn<R(CallArgs...)>::operator()(CallArgs&&... args) const& noexcept {
+R BoxFn<R(CallArgs...)>::operator()(CallArgs... args) const& noexcept {
   using Super = BoxFnOnce<R(CallArgs...)>;
   switch (Super::type_) {
     case __private::BoxFnPointer:

subspace/fn/box_fn_unittest.cc

@@ -190,14 +190,25 @@ concept can_run = requires (
 };
 // clang-format on
 
-// Receiving by-value means it must be passed as a mutable move. This means no
-// implicit copy will happen.
+// Int is copyable, so references are copied when passed.
 static_assert(can_run<void, int, int>);
 static_assert(can_run<void, int, int&&>);
-static_assert(!can_run<void, int, int&>);
-static_assert(!can_run<void, int, const int>);
-static_assert(!can_run<void, int, const int&>);
-static_assert(!can_run<void, int, const int&&>);
+static_assert(can_run<void, int, int&>);
+static_assert(can_run<void, int, const int>);
+static_assert(can_run<void, int, const int&>);
+static_assert(can_run<void, int, const int&&>);
+// But for a move-only type, it can only be passed along as a reference or an
+// rvalue.
+static_assert(can_run<void, MoveOnly, MoveOnly>);
+static_assert(can_run<void, MoveOnly, MoveOnly&&>);
+static_assert(!can_run<void, MoveOnly, MoveOnly&>);
+static_assert(!can_run<void, MoveOnly, const MoveOnly>);
+static_assert(!can_run<void, MoveOnly, const MoveOnly&>);
+static_assert(!can_run<void, MoveOnly, const MoveOnly&&>);
+static_assert(can_run<void, const MoveOnly&, MoveOnly&>);
+static_assert(can_run<void, const MoveOnly&, const MoveOnly&>);
+static_assert(can_run<void, MoveOnly&, MoveOnly&>);
+static_assert(!can_run<void, MoveOnly&, const MoveOnly&>);
 
 // Receiving a mutable reference means it must be passed as a mutable reference.
 static_assert(can_run<void, int&, int&>);