impl Add<char> and AddAssign<char> for String

Author: Ruster-a11y

src/liballoc/string.rs

@@ -1982,6 +1982,123 @@ impl Add<&str> for String {
     }
 }
 
+#[allow(missing_docs)]
+#[stable(feature = "add_string_and_dbl_ref_str", since = "1.41.0")]
+impl Add<&&str> for String {
+    type Output = String;
+
+    #[inline]
+    fn add(mut self, other: &&str) -> String {
+        self.push_str(other);
+        self
+    }
+}
+
+/// Implements the `+` operator for concatenating two `String`s.
+///
+/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
+/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
+/// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
+/// repeated concatenation.
+///
+/// The string on the right-hand side is only borrowed; its contents are copied into the returned
+/// `String`.
+///
+/// # Examples
+///
+/// Concatenating two `String`s takes the first by value and borrows the second:
+///
+/// ```
+/// let a = String::from("hello");
+/// let b = String::from(" world");
+/// let c = a + &b;
+/// // `a` is moved and can no longer be used here.
+/// ```
+///
+/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
+///
+/// ```
+/// let a = String::from("hello");
+/// let b = String::from(" world");
+/// let c = a.clone() + &b;
+/// // `a` is still valid here.
+/// ```
+///
+/// Concatenating `&str` slices can be done by converting the first to a `String`:
+///
+/// ```
+/// let a = "hello";
+/// let b = " world";
+/// let c = a.to_string() + b;
+/// ```
+#[stable(feature = "add_string_and_ref_string", since = "1.41.0")]
+impl Add<&String> for String {
+    type Output = String;
+
+    #[inline]
+    fn add(mut self, other: &String) -> String {
+        self.push_str(other);
+        self
+    }
+}
+
+#[allow(missing_docs)]
+#[stable(feature = "add_string_and_dbl_ref_string", since = "1.41.0")]
+impl Add<&&String> for String {
+    type Output = String;
+
+    #[inline]
+    fn add(mut self, other: &&String) -> String {
+        self.push_str(other);
+        self
+    }
+}
+
+/// Implements the `+` operator for concatenating a string and a char together.
+///
+/// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
+/// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
+/// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
+/// repeated concatenation.
+///
+/// # Examples
+///
+/// Concatenating a `String` with a `char` takes the `String` by value and copies the `char`:
+///
+/// ```
+/// let a = String::from("hello world! ");
+/// let b = '👋';
+/// let c = a + b;
+/// // `a` is moved and can no longer be used here.
+/// ```
+///
+/// If you want to keep using the initial `String`, you can clone it and append to the clone instead:
+///
+/// ```
+/// let a = String::from("hello world! ");
+/// let b = '👋';
+/// let c = a.clone() + b;
+/// // `a` is still valid here.
+/// ```
+///
+/// Concatenating `char` to a `&str` slice can be done by converting the `&str` to a `String`:
+///
+/// ```
+/// let a = "hello world! ";
+/// let b = '👋';
+/// let c = a.to_string() + b;
+/// ```
+#[stable(feature = "add_string_and_char", since = "1.41.0")]
+impl Add<char> for String {
+    type Output = String;
+
+    #[inline]
+    fn add(mut self, other: char) -> String {
+        self.push(other);
+        self
+    }
+}
+
 /// Implements the `+=` operator for appending to a `String`.
 ///
 /// This has the same behavior as the [`push_str`][String::push_str] method.
@@ -1993,6 +2110,28 @@ impl AddAssign<&str> for String {
     }
 }
 
+/// Implements the `+=` operator for appending to a `String`.
+///
+/// This has the same behavior as the [`push_str`][String::push_str] method.
+#[stable(feature = "stringaddassign_string", since = "1.41.0")]
+impl AddAssign<&String> for String {
+    #[inline]
+    fn add_assign(&mut self, other: &String) {
+        self.push_str(other);
+    }
+}
+
+/// Implements the `+=` operator for appending a `char` to a `String`.
+///
+/// This has the same behavior as the [`push`][String::push] method.
+#[stable(feature = "stringaddassign_char", since = "1.41.0")]
+impl AddAssign<char> for String {
+    #[inline]
+    fn add_assign(&mut self, other: char) {
+        self.push(other);
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Index<ops::Range<usize>> for String {
     type Output = str;

src/libsyntax/parse/parser/expr.rs

@@ -1084,7 +1084,9 @@ impl<'a> Parser<'a> {
                 if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
                         = next_token.kind {
                     if self.token.span.hi() == next_token.span.lo() {
-                        let s = String::from("0.") + &symbol.as_str();
+                        // FIXME: Should just be `&symbol.as_str()` but can't as of now due to Deref coercion
+                        // Issue: https://github.com/rust-lang/rust/issues/51916
+                        let s = String::from("0.") + &symbol.as_str().get_str();
                         let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
                         return Some(Token::new(kind, self.token.span.to(next_token.span)));
                     }

src/libsyntax_pos/symbol.rs

@@ -1104,6 +1104,15 @@ pub struct SymbolStr {
     string: &'static str,
 }
 
+/// FIXME: This is not needed once we are able to fix the Deref coercion issue.
+/// Issue: https://github.com/rust-lang/rust/issues/51916
+impl SymbolStr {
+    #[inline]
+    pub fn get_str(&self) -> &str {
+        self.string
+    }
+}
+
 // This impl allows a `SymbolStr` to be directly equated with a `String` or
 // `&str`.
 impl<T: std::ops::Deref<Target = str>> std::cmp::PartialEq<T> for SymbolStr {
@@ -1120,6 +1129,11 @@ impl !Sync for SymbolStr {}
 /// - `&*ss` is a `&str`;
 /// - `&ss as &str` is a `&str`, which means that `&ss` can be passed to a
 ///   function expecting a `&str`.
+/// 
+/// FIXME: This has no meaning anymore since the addition of implementations
+/// of `Add<char> for String`, `Add<&&str> for String`, and `Add<&&String> for String`.
+/// Due to the outstanding Deref coercion issue this Deref implementation gets ignored.
+/// Issue: https://github.com/rust-lang/rust/issues/51916
 impl std::ops::Deref for SymbolStr {
     type Target = str;
     #[inline]