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//! Helper macros.

/// Create an object with the given capability.
///
/// ```ignore
/// use kernel::capabilities::ProcessManagementCapability;
/// use kernel;
///
/// let process_mgmt_cap = create_capability!(ProcessManagementCapability);
/// ```
///
/// This helper macro cannot be called from `#![forbid(unsafe_code)]` crates,
/// and is used by trusted code to generate a capability that it can either use
/// or pass to another module.
#[macro_export]
macro_rules! create_capability {
    ($T:ty $(,)?) => {{
        struct Cap;
        #[allow(unsafe_code)]
        unsafe impl $T for Cap {}
        Cap
    };};
}

/// Count the number of passed expressions.
/// Useful for constructing variable sized arrays in other macros.
/// Taken from the Little Book of Rust Macros
///
/// ```ignore
/// use kernel:count_expressions;
///
/// let count: usize = count_expressions!(1+2, 3+4);
/// ```
#[macro_export]
macro_rules! count_expressions {
    () => (0usize);
    ($head:expr $(,)?) => (1usize);
    ($head:expr, $($tail:expr),* $(,)?) => (1usize + count_expressions!($($tail),*));
}