Add WithOutput trait

Author: OpenByteDev

src/conversion.rs

@@ -3,7 +3,7 @@ use crate::{
     marker::{self, Safe, Unsafe},
 };
 
-/// Helper trait to change the ABI of a function pointer type while preserving arity, safety, and signature.
+/// Helper trait to change the ABI of a function pointer type while preserving arity, safety, signature, etc.
 pub trait WithAbi<Abi>: FnPtr
 where
     Abi: marker::Abi,
@@ -18,7 +18,7 @@ where
         > + HasAbi<Abi>;
 }
 
-/// Helper trait to change the safety of a function pointer type while preserving arity, ABI, and signature.
+/// Helper trait to change the safety of a function pointer type while preserving arity, ABI, signature, etc.
 pub trait WithSafety<Safety>: FnPtr
 where
     Safety: marker::Safety,
@@ -33,14 +33,27 @@ where
         > + HasSafety<Safety>;
 }
 
-/// Helper trait to compute the safe version of a function pointer type while preserving arity, ABI, and signature.
+/// Helper trait to compute the safe version of a function pointer type while preserving arity, ABI, signature, etc.
 pub trait AsSafe: WithSafety<Safe> {}
 impl<F: WithSafety<Safe>> AsSafe for F {}
 
-/// Helper trait to compute the unsafe version of a function pointer type while preserving arity, ABI, and signature.
+/// Helper trait to compute the unsafe version of a function pointer type while preserving arity, ABI, signature, etc.
 pub trait AsUnsafe: WithSafety<Unsafe> {}
 impl<F: WithSafety<Unsafe>> AsUnsafe for F {}
 
+/// Helper trait to change the return type of a function pointer type while preserving arguments, safety, signature, etc.
+pub trait WithOutput<T>: FnPtr {
+    /// The function pointer type with the requested return type.
+    type F: FnPtr<
+            Args = Self::Args,
+            Output = T,
+            ArityMarker = Self::ArityMarker,
+            SafetyMarker = Self::SafetyMarker,
+            AbiMarker = Self::AbiMarker,
+        >;
+}
+
+
 cfg_tt::cfg_tt! {
 /// Helper trait that simplifies generic bounds when converting between funciton pointer types.
 // using has_abi_cdecl instead of stdcall, fastcall, thiscall is to reduce compile times

src/impl.rs

@@ -102,6 +102,11 @@ macro_rules! impl_fn {
         impl<Ret: 'static, $($ty: 'static),*> $crate::StaticFnPtr for $fn_type {
         }
 
+        // WithOutput
+        #[automatically_derived]
+        impl<Output, Ret, $($ty),*> $crate::WithOutput<Output> for $fn_type {
+            type F = impl_fn!(@make_unsafe extern $call_conv fn($($ty),*) -> Output, $safety);
+        }
         // WithSafety
         #[automatically_derived]
         impl<Ret, $($ty),*> $crate::WithSafety<$crate::marker::Safe> for $fn_type {