Function is_epoch 

pub fn is_epoch<T>(epoch: T) -> Result<(), String>
where
    T: AsRef<str> + Display,

👎Deprecated since 3.1.0: This crate has been marked for formal inclusion in the Agave Unstable API. From v4.0.0 onward, the agave-unstable-api crate feature must be specified to acknowledge use of an interface that may break without warning.