14

I came across the super keyword in Solidity in the context of overriding functions. What does it do?

29

The super keyword in Solidity gives access to the immediate parent contract from which the current contract is derived. When having a contract A with a function f() that derives from B which also has a function f(), A overrides the f of B. That means that myInstanceOfA.f() will call the version of f that is implemented inside A itself, the original version implemented inside B is not visible anymore. The original function f from B (being A's parent) is thus available inside A via super.f(). Alternatively, one can explicitly specifying the parent of which one wants to call the overridden function because multiple overriding steps are possible as exemplified in the example below:

pragma solidity ^0.4.5;

contract C {
  uint u;
  function f() {
    u = 1;
  }
}

contract B is C {
  function f() {
    u = 2;
  }
}

contract A is B {
  function f() {  // will set u to 3
    u = 3;
  }
  function f1() { // will set u to 2
    super.f();
  }
  function f2() { // will set u to 2
    B.f();
  }
  function f3() { // will set u to 1
    C.f();
  }
}

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