Inheritance of purity

Jacob Carlborg doob at
Thu Feb 16 23:42:53 PST 2012

On 2012-02-17 04:15, H. S. Teoh wrote:
> On Thu, Feb 16, 2012 at 06:49:40PM -0800, Walter Bright wrote:
> [...]
>> So it occurred to me that an overriding function could *inherit* the
>> qualifiers from the overridden function. The qualifiers of the
>> overriding function would be the "tightest" of its explicit qualifiers
>> and its overridden function qualifiers. It turns out that most
>> functions are naturally pure, so this greatly eases things and
>> eliminates annoying typing.
> I like this idea.
>> I want do to this for @safe, pure, nothrow, and even const.
> Excellent!
>> I think it is semantically sound, as well. The overriding function
>> body will be semantically checked against this tightest set of
>> qualifiers.
>> What do you think?
> Semantically, it makes sense. And reducing typing is always good.
> (That's one of my pet peeves about Java: too much typing just to achieve
> something really simple. It feels like being forced to kill a mosquito
> with a laser-guided missile by specifying 3D coordinates accurate to 10
> decimal places.)
> The one disadvantage I can think of is that it will no longer be clear
> exactly what qualifiers are in effect just by looking at the function
> definition in a derived class. Which is not terrible, I suppose, but I
> can see how it might get annoying if you have to trace the overrides all
> the way up the inheritance hierarchy just to find out what qualifiers a
> function actually has.
> OTOH, if ddoc could automatically fill in the effective qualifiers, then
> this will be a non-problem. ;-)

And if ddoc could show the inheritance hierarchy as well.

/Jacob Carlborg

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