Solidity inherited constructors and calling the parent constructor

Question

I'm trying to inherit from a contract. I'm expecting the child contract to have the same constructor as the parent (or be overwritten)

pragma solidity ^0.4.2;

contract parent{
    string public name;
    function parent(string _name){
        name=_name;
    }
}

contract child is parent{}

If I try

contract child2 is parent{
    function child2(string _name){
        name=_name;
    }
}

Then the string entered at construction, that should go into name, doesn't get stored.

What's going on? How do constructors work with inheritance?
Thanks in advance.

Answer 1

The trick is in the definition of the interface for Child's constructor.

pragma solidity ^0.4.2;

contract Parent {
    
    bytes32 public name;
    
    function parent(bytes32 _name){
        name=_name;
    }
}


contract Child is Parent {
    
    function child(bytes32 _name) parent(_name) {}
    
}

An explanation of this syntax here: http://solidity.readthedocs.io/en/develop/contracts.html#arguments-for-base-constructors

Hope it helps.

Answer 2

Solidity 0.5+ has a different syntax for calling parent constructors.

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;


contract Parent {

    public string name;

    constructor(string _name) {
        name = _name;
    }
}

contract Child is Parent {

    constructor() Parent("Guybrush Threepwood")  {
         // Child construction code goes here
    }
}