place.rs.html -- source
Description: Source to the Rust file `libcore/ops/place.rs`.
Keywords: rust, rustlang, rust-lang

      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140

    // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    /// Both `PLACE <- EXPR` and `box EXPR` desugar into expressions
    /// that allocate an intermediate "place" that holds uninitialized
    /// state.  The desugaring evaluates EXPR, and writes the result at
    /// the address returned by the `pointer` method of this trait.
    ///
    /// A `Place` can be thought of as a special representation for a
    /// hypothetical `&uninit` reference (which Rust cannot currently
    /// express directly). That is, it represents a pointer to
    /// uninitialized storage.
    ///
    /// The client is responsible for two steps: First, initializing the
    /// payload (it can access its address via `pointer`). Second,
    /// converting the agent to an instance of the owning pointer, via the
    /// appropriate `finalize` method (see the `InPlace`.
    ///
    /// If evaluating EXPR fails, then it is up to the destructor for the
    /// implementation of Place to clean up any intermediate state
    /// (e.g. deallocate box storage, pop a stack, etc).
    #[unstable(feature = "placement_new_protocol", issue = "27779")]
    pub trait Place<Data: ?Sized> {
        /// Returns the address where the input value will be written.
        /// Note that the data at this address is generally uninitialized,
        /// and thus one should use `ptr::write` for initializing it.
        fn pointer(&mut self) -> *mut Data;
    }

    /// Interface to implementations of  `PLACE <- EXPR`.
    ///
    /// `PLACE <- EXPR` effectively desugars into:
    ///
    /// ```
    /// # #![feature(placement_new_protocol, box_heap)]
    /// # use std::ops::{Placer, Place, InPlace};
    /// # #[allow(non_snake_case)]
    /// # fn main() {
    /// # let PLACE = std::boxed::HEAP;
    /// # let EXPR = 1;
    /// let p = PLACE;
    /// let mut place = Placer::make_place(p);
    /// let raw_place = Place::pointer(&mut place);
    /// let value = EXPR;
    /// unsafe {
    ///     std::ptr::write(raw_place, value);
    ///     InPlace::finalize(place)
    /// }
    /// # ; }
    /// ```
    ///
    /// The type of `PLACE <- EXPR` is derived from the type of `PLACE`;
    /// if the type of `PLACE` is `P`, then the final type of the whole
    /// expression is `P::Place::Owner` (see the `InPlace` and `Boxed`
    /// traits).
    ///
    /// Values for types implementing this trait usually are transient
    /// intermediate values (e.g. the return value of `Vec::emplace_back`)
    /// or `Copy`, since the `make_place` method takes `self` by value.
    #[unstable(feature = "placement_new_protocol", issue = "27779")]
    pub trait Placer<Data: ?Sized> {
        /// `Place` is the intermediate agent guarding the
        /// uninitialized state for `Data`.
        type Place: InPlace<Data>;

        /// Creates a fresh place from `self`.
        fn make_place(self) -> Self::Place;
    }

    /// Specialization of `Place` trait supporting `PLACE <- EXPR`.
    #[unstable(feature = "placement_new_protocol", issue = "27779")]
    pub trait InPlace<Data: ?Sized>: Place<Data> {
        /// `Owner` is the type of the end value of `PLACE <- EXPR`
        ///
        /// Note that when `PLACE <- EXPR` is solely used for
        /// side-effecting an existing data-structure,
        /// e.g. `Vec::emplace_back`, then `Owner` need not carry any
        /// information at all (e.g. it can be the unit type `()` in that
        /// case).
        type Owner;

        /// Converts self into the final value, shifting
        /// deallocation/cleanup responsibilities (if any remain), over to
        /// the returned instance of `Owner` and forgetting self.
        unsafe fn finalize(self) -> Self::Owner;
    }

    /// Core trait for the `box EXPR` form.
    ///
    /// `box EXPR` effectively desugars into:
    ///
    /// ```
    /// # #![feature(placement_new_protocol)]
    /// # use std::ops::{BoxPlace, Place, Boxed};
    /// # #[allow(non_snake_case)]
    /// # fn main() {
    /// # let EXPR = 1;
    /// let mut place = BoxPlace::make_place();
    /// let raw_place = Place::pointer(&mut place);
    /// let value = EXPR;
    /// # let _: Box<_> =
    /// unsafe {
    ///     ::std::ptr::write(raw_place, value);
    ///     Boxed::finalize(place)
    /// }
    /// # ; }
    /// ```
    ///
    /// The type of `box EXPR` is supplied from its surrounding
    /// context; in the above expansion, the result type `T` is used
    /// to determine which implementation of `Boxed` to use, and that
    /// `<T as Boxed>` in turn dictates determines which
    /// implementation of `BoxPlace` to use, namely:
    /// `<<T as Boxed>::Place as BoxPlace>`.
    #[unstable(feature = "placement_new_protocol", issue = "27779")]
    pub trait Boxed {
        /// The kind of data that is stored in this kind of box.
        type Data;  /* (`Data` unused b/c cannot yet express below bound.) */
        /// The place that will negotiate the storage of the data.
        type Place: BoxPlace<Self::Data>;

        /// Converts filled place into final owning value, shifting
        /// deallocation/cleanup responsibilities (if any remain), over to
        /// returned instance of `Self` and forgetting `filled`.
        unsafe fn finalize(filled: Self::Place) -> Self;
    }

    /// Specialization of `Place` trait supporting `box EXPR`.
    #[unstable(feature = "placement_new_protocol", issue = "27779")]
    pub trait BoxPlace<Data: ?Sized> : Place<Data> {
        /// Creates a globally fresh place.
        fn make_place() -> Self;
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
↑
  Move up in search results
↓
  Move down in search results
↹
  Switch tab
⏎
  Go to active search result
+ / -
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)