API docs: macros. Part of rust-lang#29329 Standard Library Documentat…

…ion Checklist.

src/liballoc/macros.rs

@@ -8,12 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/// Creates a `Vec` containing the arguments.
+/// Creates a [`Vec`] containing the arguments.
 ///
 /// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.
 /// There are two forms of this macro:
 ///
-/// - Create a `Vec` containing a given list of elements:
+/// - Create a [`Vec`] containing a given list of elements:
 ///
 /// ```
 /// let v = vec![1, 2, 3];
@@ -22,22 +22,25 @@
 /// assert_eq!(v[2], 3);
 /// ```
 ///
-/// - Create a `Vec` from a given element and size:
+/// - Create a [`Vec`] from a given element and size:
 ///
 /// ```
 /// let v = vec![1; 3];
 /// assert_eq!(v, [1, 1, 1]);
 /// ```
 ///
 /// Note that unlike array expressions this syntax supports all elements
-/// which implement `Clone` and the number of elements doesn't have to be
+/// which implement [`Clone`] and the number of elements doesn't have to be
 /// a constant.
 ///
-/// This will use `clone()` to duplicate an expression, so one should be careful
+/// This will use `clone` to duplicate an expression, so one should be careful
 /// using this with types having a nonstandard `Clone` implementation. For
 /// example, `vec![Rc::new(1); 5]` will create a vector of five references
 /// to the same boxed integer value, not five references pointing to independently
 /// boxed integers.
+///
+/// [`Vec`]: ../std/vec/struct.Vec.html
+/// [`Clone`]: ../std/clone/trait.Clone.html
 #[cfg(not(test))]
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -67,10 +70,22 @@ macro_rules! vec {
     ($($x:expr,)*) => (vec![$($x),*])
 }
 
-/// Use the syntax described in `std::fmt` to create a value of type `String`.
-/// See [`std::fmt`][fmt] for more information.
+/// Creates a `String` using interpolation of runtime expressions.
+///
+/// The first argument `format!` recieves is a format string.  This must be a string
+/// literal.  The power of the formatting string is in the `{}`s contained.
+///
+/// Additional parameters passed to `format!` replace the `{}`s within the
+/// formatting string in the order given unless named or positional parameters
+/// are used, see [`std::fmt`][fmt] for more information.
+///
+/// A common use for `format!` is concatenation and interpolation of strings.
+/// The same convention is used with [`print!`] and [`write!`] macros,
+/// depending on the intended destination of the string.
 ///
 /// [fmt]: ../std/fmt/index.html
+/// [`print!`]: macro.print.html
+/// [`write!`]: macro.write.html
 ///
 /// # Panics
 ///

src/libcore/macros.rs

@@ -62,11 +62,13 @@ macro_rules! panic {
 /// # Custom Messages
 ///
 /// This macro has a second form, where a custom panic message can
-/// be provided with or without arguments for formatting.
+/// be provided with or without arguments for formatting.  See [`std::fmt`]
+/// for syntax for this form.
 ///
 /// [`panic!`]: macro.panic.html
 /// [`debug_assert!`]: macro.debug_assert.html
-/// [testing]: ../book/first-edition/testing.html
+/// [testing]: ../book/second-edition/ch11-01-writing-tests.html#checking-results-with-the-assert-macro
+/// [`std::fmt`]: ../std/fmt/index.html
 ///
 /// # Examples
 ///
@@ -252,13 +254,15 @@ macro_rules! debug_assert {
 /// On panic, this macro will print the values of the expressions with their
 /// debug representations.
 ///
-/// Unlike `assert_eq!`, `debug_assert_eq!` statements are only enabled in non
+/// Unlike [`assert_eq!`], `debug_assert_eq!` statements are only enabled in non
 /// optimized builds by default. An optimized build will omit all
 /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
 /// compiler. This makes `debug_assert_eq!` useful for checks that are too
 /// expensive to be present in a release build but may be helpful during
 /// development.
 ///
+/// [`assert_eq!`]: ../std/macro.assert_eq.html
+///
 /// # Examples
 ///
 /// ```
@@ -277,13 +281,15 @@ macro_rules! debug_assert_eq {
 /// On panic, this macro will print the values of the expressions with their
 /// debug representations.
 ///
-/// Unlike `assert_ne!`, `debug_assert_ne!` statements are only enabled in non
+/// Unlike [`assert_ne!`], `debug_assert_ne!` statements are only enabled in non
 /// optimized builds by default. An optimized build will omit all
 /// `debug_assert_ne!` statements unless `-C debug-assertions` is passed to the
 /// compiler. This makes `debug_assert_ne!` useful for checks that are too
 /// expensive to be present in a release build but may be helpful during
 /// development.
 ///
+/// [`assert_ne!`]: ../std/macro.assert_ne.html
+///
 /// # Examples
 ///
 /// ```
@@ -300,10 +306,9 @@ macro_rules! debug_assert_ne {
 /// Helper macro for reducing boilerplate code for matching `Result` together
 /// with converting downstream errors.
 ///
-/// Prefer using `?` syntax to `try!`. `?` is built in to the language and is
-/// more succinct than `try!`. It is the standard method for error propagation.
+/// The `?` operator was added to replace `try!` and should be used instead.
 ///
-/// `try!` matches the given `Result`. In case of the `Ok` variant, the
+/// `try!` matches the given [`Result`]. In case of the `Ok` variant, the
 /// expression has the value of the wrapped value.
 ///
 /// In case of the `Err` variant, it retrieves the inner error. `try!` then
@@ -312,7 +317,9 @@ macro_rules! debug_assert_ne {
 /// error is then immediately returned.
 ///
 /// Because of the early return, `try!` can only be used in functions that
-/// return `Result`.
+/// return [`Result`].
+///
+/// [`Result`]: ../std/result/enum.Result.html
 ///
 /// # Examples
 ///
@@ -331,20 +338,26 @@ macro_rules! debug_assert_ne {
 ///     }
 /// }
 ///
+/// // The prefered method of quick returning Errors
+/// fn write_to_file_question() -> Result<(), MyError> {
+///     let mut file = File::create("my_best_friends.txt")?;
+///     Ok(())
+/// }
+///
+/// // The previous method of quick returning Errors
 /// fn write_to_file_using_try() -> Result<(), MyError> {
 ///     let mut file = try!(File::create("my_best_friends.txt"));
 ///     try!(file.write_all(b"This is a list of my best friends."));
-///     println!("I wrote to the file");
 ///     Ok(())
 /// }
+///
 /// // This is equivalent to:
 /// fn write_to_file_using_match() -> Result<(), MyError> {
 ///     let mut file = try!(File::create("my_best_friends.txt"));
 ///     match file.write_all(b"This is a list of my best friends.") {
 ///         Ok(v) => v,
 ///         Err(e) => return Err(From::from(e)),
 ///     }
-///     println!("I wrote to the file");
 ///     Ok(())
 /// }
 /// ```
@@ -365,7 +378,7 @@ macro_rules! try {
 /// formatted according to the specified format string and the result will be passed to the writer.
 /// The writer may be any value with a `write_fmt` method; generally this comes from an
 /// implementation of either the [`std::fmt::Write`] or the [`std::io::Write`] trait. The macro
-/// returns whatever the 'write_fmt' method returns; commonly a [`std::fmt::Result`], or an
+/// returns whatever the `write_fmt` method returns; commonly a [`std::fmt::Result`], or an
 /// [`io::Result`].
 ///
 /// See [`std::fmt`] for more information on the format string syntax.
@@ -470,10 +483,20 @@ macro_rules! writeln {
 /// * Loops that dynamically terminate.
 /// * Iterators that dynamically terminate.
 ///
+/// If the determination that the code is unreachable proves incorrect, the
+/// program immediately terminates with a [`panic!`].  The function [`unreachable`],
+/// which belongs to the [`std::intrinsics`] module, informs the compilier to
+/// optimize the code out of the release version entirely.
+///
+/// [`panic!`]:  ../std/macro.panic.html
+/// [`unreachable`]: ../std/intrinsics/fn.unreachable.html
+/// [`std::intrinsics`]: ../std/intrinsics/index.html
+///
 /// # Panics
 ///
-/// This will always [panic!](macro.panic.html)
+/// This will always [`panic!`]
 ///
+/// [`panic!`]: ../std/macro.panic.html
 /// # Examples
 ///
 /// Match arms:
@@ -516,13 +539,18 @@ macro_rules! unreachable {
     });
 }
 
-/// A standardized placeholder for marking unfinished code. It panics with the
-/// message `"not yet implemented"` when executed.
+/// A standardized placeholder for marking unfinished code.
+///
+/// It panics with the message `"not yet implemented"` when executed.
 ///
 /// This can be useful if you are prototyping and are just looking to have your
 /// code typecheck, or if you're implementing a trait that requires multiple
 /// methods, and you're only planning on using one of them.
 ///
+/// # Panics
+///
+/// This macro always panics.
+///
 /// # Examples
 ///
 /// Here's an example of some in-progress code. We have a trait `Foo`: