//! Helper type for disabling memory tracking when not wanted

/// Token indicating that memory quota tracking is enabled, at both compile and runtime

///

/// If support is compiled in this is a unit.

///

/// If the `memquota` cargo feature is not enabled, this type is uninhabited.

/// Scattering values of this type around in relevant data structures

/// and parameters lists

/// allows the compiler to eliminate the unwanted code.

#[derive(Clone, Copy, Debug, PartialEq)]

pub struct EnabledToken {

    /// Make non-exhaustive even within the crate

    _hidden: (),

    /// Uninhabited if the feature isn't enabled.

    #[cfg(not(feature = "memquota"))]

    _forbid: void::Void,

}

// Avoid unused crate warning.

//

// (We can't express the right dependency condition in Cargo.toml,

// and anyway it's not worth trying to conditionally suppress the dependency.)

#[cfg(feature = "memquota")]

use void as _;

impl Eq for EnabledToken {}

impl EnabledToken {

    /// Obtain an `EnabledToken` (only available if tracking is compiled in)

    #[allow(clippy::new_without_default)] // a conditional Default impl would be rather odd

    #[cfg(feature = "memquota")]

    /// Obtain an `EnabledToken` if memory-tracking is compiled in, or `None` otherwise

    #[allow(clippy::unnecessary_wraps)] // Will be None if compiled out

    #[allow(unreachable_code)]

}