[webkit-dev] Do we have a style preference about const member functions?

Maciej Stachowiak mjs at apple.com
Tue May 31 20:44:38 PDT 2011

On May 31, 2011, at 5:55 PM, Brent Fulgham wrote:

> Hi,
> On Tue, May 31, 2011 at 4:37 PM, Maciej Stachowiak <mjs at apple.com> wrote:
>> I agree that one useful distinction is whether a particular kind of object
>> is every manipulated via const pointers or references. If we never use const
>> references/pointers to a particular kind of object, then it is probably not
>> useful to maintain const-correctness discipline for that class.
> I don't agree with this.  I see no harm in maintaining const
> correctness on objects, even if they are not currently manipulated
> through const references/pointers.  They provide clear,
> self-documenting evidence that the object design intends that certain
> methods do not visibly alter the object.
> I fail to see how abandoning const correctness can do anything but
> cause us to start missing bugs that we would otherwise have found via
> compiler errors.

It's hard for me to evaluate this in the abstract. In general I like the compiler telling me as much as possible. But there's both false positive and false negative problems with const-correctness, and a maintenance burden besides just fixing the compiler errors.

For example, the compiler does not tell you that the following implementation of Node::previousSibling() (currently in our code!) is totally wrong from the "logical const" perspective:

    Node* previousSibling() const { return m_previous; }

The correct way to do const-correctness here would require more verbosity:

    const Node* previousSibling() const { return m_previous; }
    Node* previousSibling() { return m_previous; }

And the first variant would be dead code if we don't ever actually use const node pointers.

Given your views on const-correctness discipline, what do you think is the right way to handle this situation? Note that this pattern comes up for many core DOM methods and many render tree methods.


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