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Diffstat (limited to 'src/libcore/default.rs')
| -rw-r--r-- | src/libcore/default.rs | 200 |
1 files changed, 0 insertions, 200 deletions
diff --git a/src/libcore/default.rs b/src/libcore/default.rs deleted file mode 100644 index 9a8d65cd4e0..00000000000 --- a/src/libcore/default.rs +++ /dev/null @@ -1,200 +0,0 @@ -//! The `Default` trait for types which may have meaningful default values. - -#![stable(feature = "rust1", since = "1.0.0")] - -/// A trait for giving a type a useful default value. -/// -/// Sometimes, you want to fall back to some kind of default value, and -/// don't particularly care what it is. This comes up often with `struct`s -/// that define a set of options: -/// -/// ``` -/// # #[allow(dead_code)] -/// struct SomeOptions { -/// foo: i32, -/// bar: f32, -/// } -/// ``` -/// -/// How can we define some default values? You can use `Default`: -/// -/// ``` -/// # #[allow(dead_code)] -/// #[derive(Default)] -/// struct SomeOptions { -/// foo: i32, -/// bar: f32, -/// } -/// -/// fn main() { -/// let options: SomeOptions = Default::default(); -/// } -/// ``` -/// -/// Now, you get all of the default values. Rust implements `Default` for various primitives types. -/// -/// If you want to override a particular option, but still retain the other defaults: -/// -/// ``` -/// # #[allow(dead_code)] -/// # #[derive(Default)] -/// # struct SomeOptions { -/// # foo: i32, -/// # bar: f32, -/// # } -/// fn main() { -/// let options = SomeOptions { foo: 42, ..Default::default() }; -/// } -/// ``` -/// -/// ## Derivable -/// -/// This trait can be used with `#[derive]` if all of the type's fields implement -/// `Default`. When `derive`d, it will use the default value for each field's type. -/// -/// ## How can I implement `Default`? -/// -/// Provide an implementation for the `default()` method that returns the value of -/// your type that should be the default: -/// -/// ``` -/// # #![allow(dead_code)] -/// enum Kind { -/// A, -/// B, -/// C, -/// } -/// -/// impl Default for Kind { -/// fn default() -> Self { Kind::A } -/// } -/// ``` -/// -/// # Examples -/// -/// ``` -/// # #[allow(dead_code)] -/// #[derive(Default)] -/// struct SomeOptions { -/// foo: i32, -/// bar: f32, -/// } -/// ``` -#[stable(feature = "rust1", since = "1.0.0")] -pub trait Default: Sized { - /// Returns the "default value" for a type. - /// - /// Default values are often some kind of initial value, identity value, or anything else that - /// may make sense as a default. - /// - /// # Examples - /// - /// Using built-in default values: - /// - /// ``` - /// let i: i8 = Default::default(); - /// let (x, y): (Option<String>, f64) = Default::default(); - /// let (a, b, (c, d)): (i32, u32, (bool, bool)) = Default::default(); - /// ``` - /// - /// Making your own: - /// - /// ``` - /// # #[allow(dead_code)] - /// enum Kind { - /// A, - /// B, - /// C, - /// } - /// - /// impl Default for Kind { - /// fn default() -> Self { Kind::A } - /// } - /// ``` - #[stable(feature = "rust1", since = "1.0.0")] - fn default() -> Self; -} - -/// Return the default value of a type according to the `Default` trait. -/// -/// The type to return is inferred from context; this is equivalent to -/// `Default::default()` but shorter to type. -/// -/// For example: -/// ``` -/// #![feature(default_free_fn)] -/// -/// use std::default::default; -/// -/// #[derive(Default)] -/// struct AppConfig { -/// foo: FooConfig, -/// bar: BarConfig, -/// } -/// -/// #[derive(Default)] -/// struct FooConfig { -/// foo: i32, -/// } -/// -/// #[derive(Default)] -/// struct BarConfig { -/// bar: f32, -/// baz: u8, -/// } -/// -/// fn main() { -/// let options = AppConfig { -/// foo: default(), -/// bar: BarConfig { -/// bar: 10.1, -/// ..default() -/// }, -/// }; -/// } -/// ``` -#[unstable(feature = "default_free_fn", issue = "73014")] -#[inline] -pub fn default<T: Default>() -> T { - Default::default() -} - -/// Derive macro generating an impl of the trait `Default`. -#[rustc_builtin_macro] -#[stable(feature = "builtin_macro_prelude", since = "1.38.0")] -#[allow_internal_unstable(core_intrinsics)] -pub macro Default($item:item) { - /* compiler built-in */ -} - -macro_rules! default_impl { - ($t:ty, $v:expr, $doc:tt) => { - #[stable(feature = "rust1", since = "1.0.0")] - impl Default for $t { - #[inline] - #[doc = $doc] - fn default() -> $t { $v } - } - } -} - -default_impl! { (), (), "Returns the default value of `()`" } -default_impl! { bool, false, "Returns the default value of `false`" } -default_impl! { char, '\x00', "Returns the default value of `\\x00`" } - -default_impl! { usize, 0, "Returns the default value of `0`" } -default_impl! { u8, 0, "Returns the default value of `0`" } -default_impl! { u16, 0, "Returns the default value of `0`" } -default_impl! { u32, 0, "Returns the default value of `0`" } -default_impl! { u64, 0, "Returns the default value of `0`" } -default_impl! { u128, 0, "Returns the default value of `0`" } - -default_impl! { isize, 0, "Returns the default value of `0`" } -default_impl! { i8, 0, "Returns the default value of `0`" } -default_impl! { i16, 0, "Returns the default value of `0`" } -default_impl! { i32, 0, "Returns the default value of `0`" } -default_impl! { i64, 0, "Returns the default value of `0`" } -default_impl! { i128, 0, "Returns the default value of `0`" } - -default_impl! { f32, 0.0f32, "Returns the default value of `0.0`" } -default_impl! { f64, 0.0f64, "Returns the default value of `0.0`" } |