# lib.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/inventory-0.1.10/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    //! [![github]](https://github.com/dtolnay/inventory)&ensp;[![crates-io]](https://crates.io/crates/inventory)&ensp;[![docs-rs]](https://docs.rs/inventory)
    //!
    //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
    //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
    //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,PHN2ZyByb2xlPSJpbWciIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgdmlld0JveD0iMCAwIDUxMiA1MTIiPjxwYXRoIGZpbGw9IiNmNWY1ZjUiIGQ9Ik00ODguNiAyNTAuMkwzOTIgMjE0VjEwNS41YzAtMTUtOS4zLTI4LjQtMjMuNC0zMy43bC0xMDAtMzcuNWMtOC4xLTMuMS0xNy4xLTMuMS0yNS4zIDBsLTEwMCAzNy41Yy0xNC4xIDUuMy0yMy40IDE4LjctMjMuNCAzMy43VjIxNGwtOTYuNiAzNi4yQzkuMyAyNTUuNSAwIDI2OC45IDAgMjgzLjlWMzk0YzAgMTMuNiA3LjcgMjYuMSAxOS45IDMyLjJsMTAwIDUwYzEwLjEgNS4xIDIyLjEgNS4xIDMyLjIgMGwxMDMuOS01MiAxMDMuOSA1MmMxMC4xIDUuMSAyMi4xIDUuMSAzMi4yIDBsMTAwLTUwYzEyLjItNi4xIDE5LjktMTguNiAxOS45LTMyLjJWMjgzLjljMC0xNS05LjMtMjguNC0yMy40LTMzLjd6TTM1OCAyMTQuOGwtODUgMzEuOXYtNjguMmw4NS0zN3Y3My4zek0xNTQgMTA0LjFsMTAyLTM4LjIgMTAyIDM4LjJ2LjZsLTEwMiA0MS40LTEwMi00MS40di0uNnptODQgMjkxLjFsLTg1IDQyLjV2LTc5LjFsODUtMzguOHY3NS40em0wLTExMmwtMTAyIDQxLjQtMTAyLTQxLjR2LS42bDEwMi0zOC4yIDEwMiAzOC4ydi42em0yNDAgMTEybC04NSA0Mi41di03OS4xbDg1LTM4Ljh2NzUuNHptMC0xMTJsLTEwMiA0MS40LTEwMi00MS40di0uNmwxMDItMzguMiAxMDIgMzguMnYuNnoiPjwvcGF0aD48L3N2Zz4K
    //!
    //! <br>
    //!
    //! **Typed distributed plugin registration.**
    //!
    //! This crate provides a way to set up a plugin registry into which plugins
    //! can be registered from any source file linked into your application. There
    //! does not need to be a central list of all the plugins.
    //!
    //! # Examples
    //!
    //! Suppose we are writing a command line flags library and want to allow any
    //! source file in the application to register command line flags that are
    //! relevant to it.
    //!
    //! This is the flag registration style used by [gflags] and is better suited
    //! for large scale development than maintaining a single central list of flags,
    //! as the central list would become an endless source of merge conflicts in an
    //! application developed simultaneously by thousands of developers.
    //!
    //! [gflags]: https://gflags.github.io/gflags/
    //!
    //! ## Instantiating the plugin registry
    //!
    //! Let's use a `struct Flag` as the plugin type, which will contain the short
    //! name of the flag like `-v`, the full name like `--verbose`, and maybe other
    //! information like argument type and help text. We instantiate a plugin
    //! registry with an invocation of `inventory::collect!`.
    //!
    //! ```
    //! pub struct Flag {
    //!     short: char,
    //!     name: &'static str,
    //!     /* ... */
    //! }
    //!
    //! impl Flag {
    //!     pub fn new(short: char, name: &'static str) -> Self {
    //!         Flag { short, name }
    //!     }
    //! }
    //!
    //! inventory::collect!(Flag);
    //! ```
    //!
    //! This `collect!` call must be in the same crate that defines the plugin type.
    //! This macro does not "run" anything so place it outside of any function body.
    //!
    //! ## Registering plugins
    //!
    //! Now any crate with access to the `Flag` type can register flags as a plugin.
    //! Plugins can be registered by the same crate that declares the plugin type,
    //! or by any downstream crate.
    //!
    //! ```
    //! # struct Flag;
    //! #
    //! # impl Flag {
    //! #     fn new(short: char, name: &'static str) -> Self {
    //! #         Flag
    //! #     }
    //! # }
    //! #
    //! # inventory::collect!(Flag);
    //! #
    //! inventory::submit! {
    //!     Flag::new('v', "verbose")
    //! }
    //! #
    //! # fn main() {}
    //! ```
    //!
    //! The `submit!` macro does not "run" anything so place it outside of any
    //! function body. In particular, note that all `submit!` invocations across all
    //! source files linked into your application all take effect simultaneously. A
    //! `submit!` invocation is not a statement that needs to be called from `main`
    //! in order to execute.
    //!
    //! ## Iterating over plugins
    //!
    //! The value `inventory::iter::<T>` is an iterator with element type `&'static
    //! T` that iterates over all plugins registered of type `T`.
    //!
    //! ```
    //! # struct Flag {
    //! #     short: char,
    //! #     name: &'static str,
    //! # }
    //! #
    //! # inventory::collect!(Flag);
    //! #
    //! for flag in inventory::iter::<Flag> {
    //!     println!("-{}, --{}", flag.short, flag.name);
    //! }
    //! ```
    //!
    //! There is no guarantee about the order that plugins of the same type are
    //! visited by the iterator. They may be visited in any order.

    #![doc(html_root_url = "https://docs.rs/inventory/0.1.10")]
    #![cfg_attr(not(inventory_require_std), no_std)]

    #[cfg(not(inventory_require_std))]
    extern crate alloc;
    #[cfg(not(inventory_require_std))]
    use alloc::boxed::Box;

    // Not public API.
    #[doc(hidden)]
    pub use ctor::ctor;

    // Not public API.
    #[doc(hidden)]
    pub use inventory_impl as r#impl;

    use core::ops::Deref;
    use core::ptr;
    use core::sync::atomic::{AtomicPtr, Ordering};

    // Not public API. Used by generated code.
    #[doc(hidden)]
    pub struct Registry<T: 'static> {
        head: AtomicPtr<Node<T>>,
    }

    struct Node<T: 'static> {
        value: T,
        next: Option<&'static Node<T>>,
    }

    /// Trait bound corresponding to types that can be iterated by inventory::iter.
    ///
    /// This trait cannot be implemented manually. Instead use the [`collect`] macro
    /// which expands to an implementation of this trait for the given type.
    ///
    /// # Examples
    ///
    /// ```
    /// use inventory::Collect;
    ///
    /// fn count_plugins<T: Collect>() -> usize {
    ///     inventory::iter::<T>.into_iter().count()
    /// }
    /// ```
    pub trait Collect: Sized + 'static {
        #[doc(hidden)]
        fn registry() -> &'static Registry<Self>;
    }

    // Not public API. Used by generated code.
    #[doc(hidden)]
    pub fn submit<T: Collect>(value: T) {
        // TODO: Avoid allocation by storing node in a static mut Option<Node<T>>
        // after existential type is stable. See comment in inventory-impl.
        T::registry().submit(Box::new(Node { value, next: None }));
    }

    impl<T: 'static> Registry<T> {
        // Not public API. Used by generated code.
        pub const fn new() -> Self {
            Registry {
                head: AtomicPtr::new(ptr::null_mut()),
            }
        }

        fn submit(&'static self, new: Box<Node<T>>) {
            let mut new = ptr::NonNull::from(Box::leak(new));
            let mut head = self.head.load(Ordering::SeqCst);
            loop {
                // `new` is always a valid Node<T>, and is not yet visible through the registry.
                // `head` is always null or valid &'static Node<T>.
                unsafe { new.as_mut().next = head.as_ref() };
                let prev = self
                    .head
                    .compare_and_swap(head, new.as_ptr(), Ordering::SeqCst);
                if prev == head {
                    return;
                } else {
                    head = prev;
                }
            }
        }
    }

    #[allow(non_camel_case_types)]
    mod private {
        use ghost::phantom;

        #[phantom]
        pub struct iter<T>;
    }

    /// An iterator over plugins registered of a given type.
    ///
    /// The value `inventory::iter::<T>` is an iterator with element type `&'static
    /// T`.
    ///
    /// There is no guarantee about the order that plugins of the same type are
    /// visited by the iterator. They may be visited in any order.
    ///
    /// # Examples
    ///
    /// ```
    /// # struct Flag {
    /// #     short: char,
    /// #     name: &'static str,
    /// # }
    /// #
    /// # inventory::collect!(Flag);
    /// #
    /// # const IGNORE: &str = stringify! {
    /// use my_flags::Flag;
    /// # };
    ///
    /// fn main() {
    ///     for flag in inventory::iter::<Flag> {
    ///         println!("-{}, --{}", flag.short, flag.name);
    ///     }
    /// }
    /// ```
    ///
    /// Refer to the [crate level documentation](index.html) for a complete example
    /// of instantiating a plugin registry and submitting plugins.
    #[allow(non_camel_case_types)]
    pub type iter<T> = private::iter<T>;

    #[doc(hidden)]
    pub use crate::private::*;

    const ITER: () = {
        fn into_iter<T: Collect>() -> Iter<T> {
            let head = T::registry().head.load(Ordering::SeqCst);
            Iter {
                // Head pointer is always null or valid &'static Node<T>.
                node: unsafe { head.as_ref() },
            }
        }

        impl<T: Collect> IntoIterator for iter<T> {
            type Item = &'static T;
            type IntoIter = Iter<T>;

            fn into_iter(self) -> Self::IntoIter {
                into_iter()
            }
        }

        #[doc(hidden)]
        impl<T: Collect> Deref for iter<T> {
            type Target = fn() -> Iter<T>;
            fn deref(&self) -> &Self::Target {
                &(into_iter as fn() -> Iter<T>)
            }
        }

        #[derive(Clone)]
        pub struct Iter<T: 'static> {
            node: Option<&'static Node<T>>,
        }

        impl<T: 'static> Iterator for Iter<T> {
            type Item = &'static T;

            fn next(&mut self) -> Option<Self::Item> {
                let node = self.node?;
                let value = &node.value;
                self.node = node.next;
                Some(value)
            }
        }
    };

    /// Associate a plugin registry with the specified type.
    ///
    /// This call must be in the same crate that defines the plugin type. This macro
    /// does not "run" anything so place it outside of any function body.
    ///
    /// # Examples
    ///
    /// Suppose we are writing a command line flags library and want to allow any
    /// source file in the application to register command line flags that are
    /// relevant to it.
    ///
    /// This is the flag registration style used by [gflags] and is better suited
    /// for large scale development than maintaining a single central list of flags,
    /// as the central list would become an endless source of merge conflicts.
    ///
    /// [gflags]: https://gflags.github.io/gflags/
    ///
    /// ```
    /// pub struct Flag {
    ///     short: char,
    ///     name: &'static str,
    ///     /* ... */
    /// }
    ///
    /// inventory::collect!(Flag);
    /// ```
    ///
    /// Refer to the [crate level documentation](index.html) for a complete example
    /// of submitting plugins and iterating a plugin registry.
    #[macro_export]
    macro_rules! collect {
        ($ty:ty) => {
            impl $crate::Collect for $ty {
                #[inline]
                fn registry() -> &'static $crate::Registry<Self> {
                    static REGISTRY: $crate::Registry<$ty> = $crate::Registry::new();
                    &REGISTRY
                }
            }
        };
    }

    /// Enter an element into the plugin registry corresponding to its type.
    ///
    /// This call may be in the same crate that defines the type, or downstream in
    /// any crate that depends on that crate.
    ///
    /// This macro does not "run" anything so place it outside of any function body.
    /// In particular, note that all `submit!` invocations across all source files
    /// linked into your application all take effect simultaneously. A `submit!`
    /// invocation is not a statement that needs to be called from `main` in order
    /// to execute.
    ///
    /// # Examples
    ///
    /// Put `submit!` invocations outside of any function body.
    ///
    /// ```
    /// # struct Flag;
    /// #
    /// # impl Flag {
    /// #     fn new(short: char, name: &'static str) -> Self {
    /// #         Flag
    /// #     }
    /// # }
    /// #
    /// # inventory::collect!(Flag);
    /// #
    /// inventory::submit! {
    ///     Flag::new('v', "verbose")
    /// }
    /// #
    /// # fn main() {}
    /// ```
    ///
    /// Do not try to invoke `submit!` from inside of a function body as it does not
    /// do what you want.
    ///
    /// ```compile_fail
    /// // Do not do this.
    /// fn submit_flags(has_verbose_flag: bool) {
    ///     if has_verbose_flag {
    ///         inventory::submit! {
    ///             Flag::new('v', "verbose")
    ///         }
    ///     }
    /// }
    /// ```
    ///
    /// Refer to the [crate level documentation](index.html) for a complete example
    /// of instantiating and iterating a plugin registry.
    #[macro_export]
    macro_rules! submit {
        ($($value:tt)*) => {
            $crate::r#impl::submit! {
                $($value)*
            }
        }
    }

    #[allow(dead_code)]
    fn unused() {
        let _ = ITER;
    }