Macro chars 

macro_rules! chars {
    ( $low:tt .. $high:tt ) => { ... };
    ( $low:tt ..= $high:tt ) => { ... };
    ( .. ) => { ... };
}

Convenience macro for the initialization of CharRanges.

Syntax

chars!('a'..'z'); // The half open range including 'a' and excluding 'z'
chars!('a'..='z'); // The closed range including 'a' and including 'z'
chars!(..); // All characters

chars!('a'..='z') and chars!(..) are constant-time expressions, and can be used where such are required, such as in the initialization of constant data structures.

NOTE: Because an expr capture cannot be followed by a ../..=, this macro captures token trees. This means that if you want to pass more than one token, you must parenthesize it (e.g. chars!('\0' ..= (char::MAX))).