Add std feature and std::error::Error impl

Cargo.toml

@@ -19,3 +19,6 @@ rust-version = "1.65"
 [dependencies]
 typenum = "1.17"
 zeroize = { version = "1.7", optional = true }
+
+[features]
+std = []

src/iter.rs

@@ -2,13 +2,25 @@
 //! functionality.
 
 use crate::{Array, ArraySize};
-use core::slice::{Iter, IterMut};
+use core::{
+    fmt,
+    slice::{Iter, IterMut},
+};
 
 /// Couldn't construct an array from an iterator because the number of items in the iterator
 /// didn't match the array size.
 #[derive(Clone, Copy, Debug)]
 pub struct TryFromIteratorError;
 
+impl fmt::Display for TryFromIteratorError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("iterator did not contain the correct number of items for the array size")
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for TryFromIteratorError {}
+
 impl<T, U> Array<T, U>
 where
     U: ArraySize,

src/lib.rs

@@ -1,5 +1,5 @@
 #![no_std]
-#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
@@ -23,6 +23,9 @@
     unused_qualifications
 )]
 
+#[cfg(feature = "std")]
+extern crate std;
+
 mod from_fn;
 mod iter;
 mod sizes;