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//! 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,
}
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")]
pub const fn new() -> Self {
EnabledToken { _hidden: () }
}
/// 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)]
pub const fn new_if_compiled_in() -> Option<Self> {
Some(EnabledToken {
_hidden: (),
#[cfg(not(feature = "memquota"))]
_forbid: return None,
})
}
}
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