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(){

Leads to error

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

1 Answer 1


Have your code changed as below

function inc(Data storage self) internal{

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

  • 1
    wow didn't know, need to check this Monday, must go to the F1 race with my father this tomorrow Commented Jul 2, 2016 at 19:18

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