Derive Macro IndexMut 

#[derive(IndexMut)]
{
    // Attributes available to this derive:
    #[index_mut]
}

Implement IndexMut for a structure.

Sample.

use derive_tools::IndexMut;

#[ derive( IndexMut ) ]
struct MyStruct( i32 );

let mut my_struct = MyStruct( 13 );
my_struct[ 0 ] += 1;
dbg!( my_struct.0 );

To learn more about the feature, study the module derive_tools::IndexMut.