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//! Defines `Relevant` type to use in types that requires
//! custom destruction.
//!
//! With default feature "std" it `Drop` implementation will not trigger panic
//! in case of unwinding (e.g. already panicking).
//! 

#![cfg_attr(not(feature = "std"), no_std)]

/// Values of this type can't be automatically dropped.
/// If struct or enum has field with type `Relevant`,
/// it can't be automatically dropped either. And so considered relevant too.
/// User has to deconstruct such values and call `Relevant::dispose`.
/// If relevant field is private it means that user has to move value into some public method.
/// For example `memory::Block` should be returned to the `MemoryAllocator` it came from.
/// 
/// User of the engine won't usually deal with real relevant types.
/// More often user will face wrappers that has backdoor - some technique
/// to dispose internal relevant fields with runtime cost.
/// In debug mode such wrappers can put warnings in log.
/// So that user will know they should be disposed manually.
/// 
/// # Panics
/// 
/// Panics when dropped.
/// 
#[derive(Clone, Debug, PartialOrd, PartialEq, Ord, Eq, Hash)]
pub struct Relevant;

impl Relevant {
    /// Dispose this value.
    #[cfg(feature = "std")]
    pub fn dispose(self) {
        ::std::mem::forget(self)
    }

    #[cfg(not(feature = "std"))]
    pub fn dispose(self) {
        ::core::mem::forget(self)
    }
}

impl Drop for Relevant {

    #[cfg(feature = "std")]
    fn drop(&mut self) {
        if !::std::thread::panicking() {
            panic!("Values of this type can't be dropped!")
        }
    }

    #[cfg(not(feature = "std"))]
    fn drop(&mut self) {
        panic!("Values of this type can't be dropped!")
    }
}