implement FromIterator<char> for Box<str>

src/liballoc/boxed.rs

@@ -95,6 +95,7 @@ use core::task::{Context, Poll};
 use crate::alloc::{self, Global, Alloc};
 use crate::vec::Vec;
 use crate::raw_vec::RawVec;
+use crate::string::String;
 use crate::str::from_boxed_utf8_unchecked;
 
 /// A pointer type for heap allocation.
@@ -1070,3 +1071,12 @@ impl<F: ?Sized + Future + Unpin> Future for Box<F> {
         F::poll(Pin::new(&mut *self), cx)
     }
 }
+
+#[unstable(feature = "box_str_from_iter", issue = "0")]
+impl FromIterator<char> for Box<str> {
+    fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> Box<str> {
+        let mut buf = String::new();
+        buf.extend(iter);
+        buf.into_boxed_str()
+    }
+}

src/liballoc/tests.rs

@@ -9,6 +9,7 @@ use core::f64;
 use core::i64;
 
 use std::boxed::Box;
+use std::string::String;
 
 #[test]
 fn test_owned_clone() {
@@ -151,3 +152,12 @@ fn test_array_from_slice() {
     let a: Result<Box<[u32; 2]>, _> = r.clone().try_into();
     assert!(a.is_err());
 }
+
+#[test]
+fn box_str_from_iter(){
+    let iter = (0..100).map(|_|{'☺'});
+    let string: Box<str> = iter.collect();
+
+    assert_eq!(string.len(), 100);
+    assert_eq!(string.chars().nth(5), '☺');
+}