minimo/
lazy.rs

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#![no_std]

extern crate alloc;

use alloc::sync::Arc;
use core::cell::UnsafeCell;
use core::ops::Deref;
use core::sync::atomic::{AtomicBool, Ordering};
use alloc::boxed::Box;

pub struct Lazy<T> {
    init: AtomicBool,
    value: UnsafeCell<Option<T>>,
}

unsafe impl<T: Send + Sync> Sync for Lazy<T> {}

impl<T> Lazy<T> {
    pub const INIT: Self = Lazy {
        init: AtomicBool::new(false),
        value: UnsafeCell::new(None),
    };

    #[inline(always)]
    pub fn get<F>(&self, init: F) -> &T
    where
        F: FnOnce() -> T,
    {
        if !self.init.load(Ordering::Acquire) {
            let value = init();
            unsafe {
                *self.value.get() = Some(value);
            }
            self.init.store(true, Ordering::Release);
        }
        unsafe { (*self.value.get()).as_ref().unwrap() }
    }

    #[inline(always)]
    pub fn get_mut<F>(&self, init: F) -> &mut T
    where
        F: FnOnce() -> T,
    {
        if !self.init.load(Ordering::Acquire) {
            let value = init();
            unsafe {
                *self.value.get() = Some(value);
            }
            self.init.store(true, Ordering::Release);
        }
        unsafe { (*self.value.get()).as_mut().unwrap() }
    }
}

pub trait LazyStatic {
    fn initialize(&self);
}

impl<T> LazyStatic for Lazy<T> {
    fn initialize(&self) {
        self.init.load(Ordering::Acquire);
    }
}

pub fn initialize<T: LazyStatic>(lazy: &T) {
    lazy.initialize();
}

#[macro_export]
macro_rules! lazy {
    ($(#[$attr:meta])* $vis:vis static ref $N:ident : $T:ty = $e:expr; $($rest:tt)*) => {
        lazy!(@single, $(#[$attr])* $vis static ref $N : $T = $e);
        lazy!($($rest)*);
    };
    (@single, $(#[$attr:meta])* $vis:vis static ref $N:ident : $T:ty = $e:expr) => {
        #[allow(non_camel_case_types)]
        $(#[$attr])*
        $vis struct $N {
            inner: $crate::Lazy<$T>,
        }
        
        impl core::ops::Deref for $N {
            type Target = $T;
            
            fn deref(&self) -> &$T {
                self.inner.get(|| $e)
            }
        }
        
        impl $N {
            #[allow(dead_code)]
            $vis fn get() -> &'static $T {
                &*$N
            }

            #[allow(dead_code)]
            $vis fn get_mut() -> &'static mut $T {
                $N.inner.get_mut(|| $e)
            }
        }
        
        $vis static $N: $N = $N { inner: $crate::Lazy::INIT };
    };
    () => ()
}

#[macro_export]
macro_rules! lazy_arc {
    ($(#[$attr:meta])* $vis:vis static ref $N:ident : Arc<$T:ty> = $e:expr; $($rest:tt)*) => {
        lazy!(@arc, $(#[$attr])* $vis static ref $N : Arc<$T> = Arc::new($e));
        lazy_arc!($($rest)*);
    };
    (@arc, $(#[$attr:meta])* $vis:vis static ref $N:ident : Arc<$T:ty> = $e:expr) => {
        lazy!(@single, $(#[$attr])* $vis static ref $N : Arc<$T> = $e);

        impl $N {
            #[allow(dead_code)]
            $vis fn get() -> Arc<$T> {
                (*$N).clone()
            }

            #[allow(dead_code)]
            $vis fn set(value: $T) {
                *$N::get_mut() = Arc::new(value);
            }
        }
    };
    () => ()
}