Should the constructor function be public?

Question

In all the tutorials I'm watching nobody specifies public, but remix presents warnings that function visibility has not been specified, and public is assumed.

Since I don't like warnings if possible, I am specifying public where necessary, but I wonder if the constructor function itself should be public or private. It seems to me that it should be a private one, as it's called automatically by the contract itself on creation, or is my reasoning faulty?

Answer 1

When you are trying to compile contract with private constructor, for example this one:

pragma solidity ^0.4.15;


contract PrivateConstructor {
    string public title;

    function PrivateConstructor() private {
        title = "Private Constructor";
    }

}

you receive this error:

TypeError: Constructor must be public or internal.

So looks like contract counstructor could be only public or internal.

More details here Visibility and Getters

Answer 2

Update for users of Solidity v0.7 (and above):

The constructor visibility has been removed from Solidity. You have to remove the "public" and the "internal" modifiers from your constructors.

Read more about this in the breaking changes list.

Answer 3

A constructor can be internal or public; however, if the constructor has a 'payable' modifier, then the constructor can only be public.

Regarding internal visibility, it makes it possible for an abstract contract to have a constructor.