Macro warn 

macro_rules! warn {
    ($self:ident, $fmt_str:literal) => { ... };
    ($self:ident, $fmt_str:literal, $($args:expr),*) => { ... };
}

A simple macro which is compatible with Rust’s format syntax used in macros like print!, println!, and format!. Prints a warning to the logger.

Note

The first argument should be self.