How to access a mapping in a library?

Question

library Lib{
    struct Data {
        mapping (uint => uint) a;
    }

    function inc(Data self) internal{
        self.a[0] =+1;
    }
}
contract Example{

    address recipient = 0x0000cafebabe;

    Lib.Data data;

    function send(){
        Lib.inc(data);
    }
}

Leads to error

7:9: Error: Member "a" is not available in struct Data memory outside of storage.
        self.a[0] =+1;
        ^----^

Answer 1

Have your code changed as below

function inc(Data storage self) internal{
        self.a[0]=+1;
    }

Note the storage part of it. Please understand the concepts of Internal Types for variables and In memory types