Refactor to reduce the amount of unsafe and duplicated code.

futures-util/Cargo.toml

@@ -46,6 +46,7 @@ memchr = { version = "2.2", optional = true }
 futures_01 = { version = "0.1.25", optional = true, package = "futures" }
 tokio-io = { version = "0.1.9", optional = true }
 pin-utils = "0.1.0-alpha.4"
+pin-project = "0.4.8"
 
 [dev-dependencies]
 futures = { path = "../futures", version = "0.3.4", features = ["async-await", "thread-pool"] }

futures-util/src/fns.rs

@@ -0,0 +1,354 @@
+use core::marker::PhantomData;
+use core::fmt::{self, Debug};
+
+pub trait FnOnce1<A> {
+    type Output;
+    fn call_once(self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> FnOnce1<A> for T
+where
+    T: FnOnce(A) -> R
+{
+    type Output = R;
+    fn call_once(self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+pub trait FnMut1<A>: FnOnce1<A> {
+    fn call_mut(&mut self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> FnMut1<A> for T
+where
+    T: FnMut(A) -> R
+{
+    fn call_mut(&mut self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+// Not used, but present for completeness
+#[allow(unreachable_pub)]
+pub trait Fn1<A>: FnMut1<A> {
+    fn call(&self, arg: A) -> Self::Output;
+}
+
+impl<T, A, R> Fn1<A> for T
+where
+    T: Fn(A) -> R
+{
+    fn call(&self, arg: A) -> R {
+        self(arg)
+    }
+}
+
+macro_rules! trivial_fn_impls {
+    ($name:ident <$($arg:ident),*> $t:ty = $debug:literal) => {
+        impl<$($arg),*> Copy for $t {}
+        impl<$($arg),*> Clone for $t {
+            fn clone(&self) -> Self { *self }
+        }
+        impl<$($arg),*> Debug for $t {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                f.write_str($debug)
+            }
+        }
+        impl<$($arg,)* A> FnMut1<A> for $t where Self: FnOnce1<A> {
+            fn call_mut(&mut self, arg: A) -> Self::Output {
+                self.call_once(arg)
+            }
+        }
+        impl<$($arg,)* A> Fn1<A> for $t where Self: FnOnce1<A> {
+            fn call(&self, arg: A) -> Self::Output {
+                self.call_once(arg)
+            }
+        }
+        pub(crate) fn $name<$($arg),*>() -> $t {
+            Default::default()
+        }
+    }
+}
+
+pub struct OkFn<E>(PhantomData<fn(E)>);
+
+impl<E> Default for OkFn<E> {
+    fn default() -> Self {
+        OkFn(PhantomData)
+    }
+}
+
+impl<A, E> FnOnce1<A> for OkFn<E> {
+    type Output = Result<A, E>;
+    fn call_once(self, arg: A) -> Self::Output {
+        Ok(arg)
+    }
+}
+
+trivial_fn_impls!(ok_fn <T> OkFn<T> = "Ok");
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct ChainFn<F, G>(F, G);
+
+impl<F, G, A> FnOnce1<A> for ChainFn<F, G>
+where
+    F: FnOnce1<A>,
+    G: FnOnce1<F::Output>,
+{
+    type Output = G::Output;
+    fn call_once(self, arg: A) -> Self::Output {
+        self.1.call_once(self.0.call_once(arg))
+    }
+}
+impl<F, G, A> FnMut1<A> for ChainFn<F, G>
+where
+    F: FnMut1<A>,
+    G: FnMut1<F::Output>,
+{
+    fn call_mut(&mut self, arg: A) -> Self::Output {
+        self.1.call_mut(self.0.call_mut(arg))
+    }
+}
+impl<F, G, A> Fn1<A> for ChainFn<F, G>
+where
+    F: Fn1<A>,
+    G: Fn1<F::Output>,
+{
+    fn call(&self, arg: A) -> Self::Output {
+        self.1.call(self.0.call(arg))
+    }
+}
+pub(crate) fn chain_fn<F, G>(f: F, g: G) -> ChainFn<F, G> {
+    ChainFn(f, g)
+}
+
+#[derive(Default)]
+pub struct MergeResultFn;
+
+impl<T> FnOnce1<Result<T, T>> for MergeResultFn {
+    type Output = T;
+    fn call_once(self, arg: Result<T, T>) -> Self::Output {
+        match arg {
+            Ok(x) => x,
+            Err(x) => x,
+        }
+    }
+}
+trivial_fn_impls!(merge_result_fn <> MergeResultFn = "merge_result");
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct InspectFn<F>(F);
+
+impl<F, A> FnOnce1<A> for InspectFn<F>
+where
+    F: for<'a> FnOnce1<&'a A, Output=()>,
+{
+    type Output = A;
+    fn call_once(self, arg: A) -> Self::Output {
+        self.0.call_once(&arg);
+        arg
+    }
+}
+impl<F, A> FnMut1<A> for InspectFn<F>
+where
+    F: for<'a> FnMut1<&'a A, Output=()>,
+{
+    fn call_mut(&mut self, arg: A) -> Self::Output {
+        self.0.call_mut(&arg);
+        arg
+    }
+}
+impl<F, A> Fn1<A> for InspectFn<F>
+where
+    F: for<'a> Fn1<&'a A, Output=()>,
+{
+    fn call(&self, arg: A) -> Self::Output {
+        self.0.call(&arg);
+        arg
+    }
+}
+pub(crate) fn inspect_fn<F>(f: F) -> InspectFn<F> {
+    InspectFn(f)
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct MapOkFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for MapOkFn<F>
+where
+    F: FnOnce1<T>,
+{
+    type Output = Result<F::Output, E>;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for MapOkFn<F>
+where
+    F: FnMut1<T>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for MapOkFn<F>
+where
+    F: Fn1<T>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.map(|x| self.0.call(x))
+    }
+}
+pub(crate) fn map_ok_fn<F>(f: F) -> MapOkFn<F> {
+    MapOkFn(f)
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct MapErrFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for MapErrFn<F>
+where
+    F: FnOnce1<E>,
+{
+    type Output = Result<T, F::Output>;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for MapErrFn<F>
+where
+    F: FnMut1<E>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for MapErrFn<F>
+where
+    F: Fn1<E>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.map_err(|x| self.0.call(x))
+    }
+}
+pub(crate) fn map_err_fn<F>(f: F) -> MapErrFn<F> {
+    MapErrFn(f)
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct InspectOkFn<F>(F);
+
+impl<'a, F, T, E> FnOnce1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: FnOnce1<&'a T, Output=()>
+{
+    type Output = ();
+    fn call_once(self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg { self.0.call_once(x) }
+    }
+}
+impl<'a, F, T, E> FnMut1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: FnMut1<&'a T, Output=()>,
+{
+    fn call_mut(&mut self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg { self.0.call_mut(x) }
+    }
+}
+impl<'a, F, T, E> Fn1<&'a Result<T, E>> for InspectOkFn<F>
+where
+    F: Fn1<&'a T, Output=()>,
+{
+    fn call(&self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Ok(x) = arg { self.0.call(x) }
+    }
+}
+pub(crate) fn inspect_ok_fn<F>(f: F) -> InspectOkFn<F> {
+    InspectOkFn(f)
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct InspectErrFn<F>(F);
+
+impl<'a, F, T, E> FnOnce1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: FnOnce1<&'a E, Output=()>
+{
+    type Output = ();
+    fn call_once(self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg { self.0.call_once(x) }
+    }
+}
+impl<'a, F, T, E> FnMut1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: FnMut1<&'a E, Output=()>,
+{
+    fn call_mut(&mut self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg { self.0.call_mut(x) }
+    }
+}
+impl<'a, F, T, E> Fn1<&'a Result<T, E>> for InspectErrFn<F>
+where
+    F: Fn1<&'a E, Output=()>,
+{
+    fn call(&self, arg: &'a Result<T, E>) -> Self::Output {
+        if let Err(x) = arg { self.0.call(x) }
+    }
+}
+pub(crate) fn inspect_err_fn<F>(f: F) -> InspectErrFn<F> {
+    InspectErrFn(f)
+}
+
+pub(crate) type MapOkOrElseFn<F, G> = ChainFn<MapOkFn<F>, ChainFn<MapErrFn<G>, MergeResultFn>>;
+pub(crate) fn map_ok_or_else_fn<F, G>(f: F, g: G) -> MapOkOrElseFn<F, G> {
+    chain_fn(map_ok_fn(f), chain_fn(map_err_fn(g), merge_result_fn()))
+}
+
+#[derive(Debug, Copy, Clone, Default)]
+pub struct UnwrapOrElseFn<F>(F);
+
+impl<F, T, E> FnOnce1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: FnOnce1<E, Output=T>,
+{
+    type Output = T;
+    fn call_once(self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call_once(x))
+    }
+}
+impl<F, T, E> FnMut1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: FnMut1<E, Output=T>,
+{
+    fn call_mut(&mut self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call_mut(x))
+    }
+}
+impl<F, T, E> Fn1<Result<T, E>> for UnwrapOrElseFn<F>
+where
+    F: Fn1<E, Output=T>,
+{
+    fn call(&self, arg: Result<T, E>) -> Self::Output {
+        arg.unwrap_or_else(|x| self.0.call(x))
+    }
+}
+pub(crate) fn unwrap_or_else_fn<F>(f: F) -> UnwrapOrElseFn<F> {
+    UnwrapOrElseFn(f)
+}
+
+pub struct IntoFn<T>(PhantomData<fn() -> T>);
+
+impl<T> Default for IntoFn<T> {
+    fn default() -> Self {
+        IntoFn(PhantomData)
+    }
+}
+impl<A, T> FnOnce1<A> for IntoFn<T> where A: Into<T> {
+    type Output = T;
+    fn call_once(self, arg: A) -> Self::Output {
+        arg.into()
+    }
+}
+
+trivial_fn_impls!(into_fn <T> IntoFn<T> = "Into::into");