AllEqualValueError implements std::error::Error

Author: phimuemue

src/all_equal_value_err.rs

@@ -1,3 +1,31 @@
-/// Value returned for the error case of `Itertools::all_equal_value()`.
+#[cfg(doc)]
+use crate::Itertools;
+#[cfg(feature = "use_std")]
+use std::error::Error;
+use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
+
+/// Value returned for the error case of [`Itertools::all_equal_value`].
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct AllEqualValueError<Item>(pub Option<[Item; 2]>);
+
+impl<Item> Display for AllEqualValueError<Item> {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        match self.0 {
+            None => {
+                write!(
+                    f,
+                    "got zero elements when all elements were expected to be equal"
+                )
+            }
+            Some([_, _]) => {
+                write!(
+                    f,
+                    "got different elements when all elements were expected to be equal"
+                )
+            }
+        }
+    }
+}
+
+#[cfg(feature = "use_std")]
+impl<Item> Error for AllEqualValueError<Item> where Item: Debug {}