cross: list: add IntoVec trait

crates/cross/src/compound/list/mod.rs

@@ -240,6 +240,33 @@ where
     }
 }
 
+
+#[cfg(feature = "std")]
+mod into_vec {
+    use super::*;
+    pub struct IntoVecOp;
+    impl<Next> FoldOp<Vec<Next>, Next> for IntoVecOp {
+        type Output = Vec<Next>;
+        fn feed(&mut self, mut prev: Vec<Next>, next: Next) -> Self::Output {
+            prev.push(next);
+            prev
+        }
+    }
+    pub trait IntoVec<T> {
+        fn into_vec(self) -> Vec<T>;
+    }
+    impl<T, L> IntoVec<T> for L
+    where
+        L: Fold<IntoVecOp, Vec<T>, Output=Vec<T>>
+    {
+        fn into_vec(self) -> Vec<T> {
+            self.fold(IntoVecOp, Vec::new())
+        }
+    }
+}
+#[cfg(feature = "std")]
+pub use into_vec::{IntoVec, IntoVecOp};
+
 pub trait MapVisitor<V> {
     type Output;
     fn map(&self, elem: V) -> Self::Output;
@@ -502,6 +529,23 @@ mod test {
         assert_eq!(v.0, 24);
     }
 
+    #[test]
+    fn into_vec() {
+        let list = (3i32, 4i32, 5i32).into_list();
+        assert_eq!(list.into_vec(), vec![3i32, 4, 5]);
+    }
+
+    #[test]
+    fn into_vec_ref() {
+        let list = &(3i32, 4i32, 5i32).into_list();
+        assert_eq!(list.into_vec(), vec![&3i32, &4, &5]);
+    }
+
+    #[test]
+    fn into_vec_empty() {
+        assert_eq!(IntoVec::<u32>::into_vec(Empty::default()), vec![]);
+    }
+
     #[test]
     fn sum() {
         let list = (3i32, 4i32, 5i32).into_list();

crates/cross/src/lib.rs

@@ -1,5 +1,5 @@
-#![no_std]
 #![feature(core_intrinsics)]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 pub mod compound;
 pub mod dim;