// Note that underscore usage depends on context, see link at bottom (not source)
Underscores are used in front of variables to tell the compiler that you don't
plan on using the variable.
Example, two cases, comment explains what compiler does
let mut my_variable:u32 = 18;        // Compiler will warn you about an unused variable
let mut _my_variable:u32 = 18;        // Compiler will say nothing

// Context link: https://runrust.miraheze.org/wiki/Underscore