Re: Inheritance and in-contracts

[aldanor via Digitalmars-d-learn]

https://github.com/D-Programming-Language/dmd/pull/4200

Re: Inheritance and in-contracts

[aldanor via Digitalmars-d-learn]

On Monday, 22 December 2014 at 19:11:13 UTC, Ali Çehreli wrote:

On 12/22/2014 10:06 AM, aldanor wrote:

https://github.com/D-Programming-Language/dmd/pull/4200


Thank you! This fixes a big problem with the contracts in D.

Ali


It's not my PR but I just thought this thread would be happy to 
know :)

Re: Inheritance and in-contracts

[Ali Çehreli via Digitalmars-d-learn]

On 12/22/2014 10:06 AM, aldanor wrote:

https://github.com/D-Programming-Language/dmd/pull/4200


Thank you! This fixes a big problem with the contracts in D.

Ali

Re: Inheritance and in-contracts

[Joseph Rushton Wakeling via Digitalmars-d-learn]

On 22/12/14 19:06, aldanor via Digitalmars-d-learn wrote:

https://github.com/D-Programming-Language/dmd/pull/4200


Yes, I saw that PR with some joy -- thanks for the link! :-)

Re: Inheritance and in-contracts

[Joseph Rushton Wakeling via Digitalmars-d-learn]

On 22/12/14 20:12, aldanor via Digitalmars-d-learn wrote:

On Monday, 22 December 2014 at 19:11:13 UTC, Ali Çehreli wrote:

On 12/22/2014 10:06 AM, aldanor wrote:

https://github.com/D-Programming-Language/dmd/pull/4200


Thank you! This fixes a big problem with the contracts in D.

Ali


It's not my PR but I just thought this thread would be happy to know :)


Actually, the author is a friend of mine, and an all-round wonderful guy. :-)

Inheritance and in-contracts

[Joseph Rushton Wakeling via Digitalmars-d-learn]

Suppose I have a base class where one of the methods has an in-contract, and a 
derived class that overrides it:


/
import std.stdio;

abstract class Base
{
abstract void foo(int n)
in
{
assert(n  5);
}
body
{
assert(false, Shouldn't get here);
}
}

class Deriv : Base
{
override void foo(int n)
{
writeln(n = , n);
}
}


void main()
{
Base b = new Deriv;

b.foo(7);
b.foo(3);
}
/

This outputs,

n = 7
n = 3

In other words, the lack of explicit in-contract on Deriv.foo is being taken as 
an _empty_ in-contract, which is being interpreted as per the rule that a 
derived class can have a less restrictive contract than its base (cf. TDPL 
pp.329-331).


Question: is there any way of indicating that Deriv.foo should inherit the 
in-contract from the base method, without actually calling super.foo ... ?


Following the example on p.331, I did try calling super.__in_contract_format(n) 
(... or this.Base.__in_contract_format(n) or other variants), but that doesn't 
seem to work:


Error: no property '__in_contract_foo' for type 'incontract.Base'

... so can anyone advise if there is a reasonable way of achieving this?

Thanks,

 -- Joe

Re: Inheritance and in-contracts

[Ali Çehreli via Digitalmars-d-learn]

On 12/05/2014 02:39 PM, Joseph Rushton Wakeling via Digitalmars-d-learn 
wrote:


 In other words, the lack of explicit in-contract on Deriv.foo is being
 taken as an _empty_ in-contract, which is being interpreted as per the
 rule that a derived class can have a less restrictive contract than its
 base (cf. TDPL pp.329-331).

This is a known problem with contract inheritance. The following bug 
report mentions the ugly hack of defining assert(0) as the derived's 
'in' contract:


  https://issues.dlang.org/show_bug.cgi?id=6856

Ali

Re: Inheritance and in-contracts

[bearophile via Digitalmars-d-learn]

Joseph Rushton Wakeling:

Suppose I have a base class where one of the methods has an 
in-contract,


It's named precondition or pre-condition.


Following the example on p.331, I did try calling 
super.__in_contract_format(n) (... or 
this.Base.__in_contract_format(n) or other variants), but that 
doesn't seem to work:


Error: no property '__in_contract_foo' for type 
'incontract.Base'


... so can anyone advise if there is a reasonable way of 
achieving this?


Is this a strong need?

Bye,
bearophile

Re: Inheritance and in-contracts

[Joseph Rushton Wakeling via Digitalmars-d-learn]

On 05/12/14 23:45, Ali Çehreli via Digitalmars-d-learn wrote:

This is a known problem with contract inheritance. The following bug report
mentions the ugly hack of defining assert(0) as the derived's 'in' contract:

   https://issues.dlang.org/show_bug.cgi?id=6856


Thanks for the clarification.  This is a not-nice situation; FWIW I would second 
Don's proposal that the absence of an explicit in-contract on the derived-class 
method ought to indicate inheritance of the base contract.


I guess the assert(false) method will do, but I find it as ugly as you do :-(

One further annoyance, pointed out to me by a colleague earlier today: given 
that base and derived in-contracts basically come down to,


   try
   {
   Base.in()
   }
   catch (Throwable)
   {
  Derived.in()
   }

... aren't there some nasty consequences here for memory allocation and the 
generation of garbage?

Re: Inheritance and in-contracts

[Joseph Rushton Wakeling via Digitalmars-d-learn]

On 06/12/14 00:24, bearophile via Digitalmars-d-learn wrote:

Is this a strong need?


Let's put it this way: I don't mind copy-pasting the same in-contract into 
derived class methods.  I'd just rather avoid it, and was hoping there was a way 
to do so which was trivial.


It's disappointing that the lack of an explicitly empty in-contract doesn't 
imply inheritance of the base contract, but I could live with it much more 
easily if I could explicitly indicate that desired inheritance.