Re: Type invariants and private extensions?

[Victor Porton <porton@narod.ru>]

Jeffrey R. Carter wrote:

> On 09/12/2017 12:02 AM, Victor Porton wrote:
>> Isn't it a good idea to modify the RM to allow type invariants also for
>> derived types with null records?
> 
> Not unless you have a real problem that can't be solved otherwise.

I do have:

A SPARQL query may return boolean, graph, bindings, etc. The return type is 
determined by the text of the query.

I want to make derived types of a query which are validated that their 
return is of a certain type (e.g. a boolean). This certainly useful in a 
language like Ada intended for reliability and maximum runtime check during 
debugging.

I could make them just private extensions instead of null record extensions, 
but after this I would be forced to manually make a derived version of every 
constructor function for the derived type.

It appeared as a real practical problem in my research.

-- 
Victor Porton - http://portonvictor.org