Macro lit_str 

macro_rules! lit_str {
    ($struct_name:ident, $val:expr) => { ... };
}

Creates a type that represents a specific string literal.

The generated type:

• Has a VALUE constant with the string
• Implements FromStr (only accepts the exact string)
• Implements Serialize/Deserialize (as the string)
• Implements Display (outputs the string)