How do you add contracts to delegates?

This doesn't work:


void main() {
    void delegate(int) foo;

    foo = (x)
    in {
        assert(x > 0);
    } body {
    };
}


Nor this:


void main() {
    void delegate(int) foo
    in {
        assert(x > 0);
    };

    foo = (x) {};
}

Bye,
bearophile

Am 08.01.2013 12:14, schrieb bearophile:
> How do you add contracts to delegates?
>
> This doesn't work:
>
>
> void main() {
>      void delegate(int) foo;
>
>      foo = (x)
>      in {
>          assert(x > 0);
>      } body {
>      };
> }
>
>
> Nor this:
>
>
> void main() {
>      void delegate(int) foo
>      in {
>          assert(x > 0);
>      };
>
>      foo = (x) {};
> }
>
> Bye,
> bearophile

I don't think that this is possible at all. Do you think this is usefull?

Kind Regards
Benjamin Thaut

Benjamin Thaut:

> I don't think that this is possible at all.

I see.


> Do you think this is usefull?

In a program I define a null delegate, then later I assign to it one of different functions according to some run time values, and later I call the delegate several times. In such situation a delegate is handy to shorten my code, where max performance is not needed.

I generally use contract programming, because I've seen it catches some of my coding mistakes. So what's wrong in desiring to add a pre-condition to that delegate? (Currently I have put the pre-condition asserts inside the function assigned to the delegate).

Bye,
bearophile

08-Jan-2013 17:58, bearophile пишет:
> Benjamin Thaut:
>
>> I don't think that this is possible at all.
>
> I see.
>
>
>> Do you think this is usefull?
>
> In a program I define a null delegate, then later I assign to it one of
> different functions according to some run time values, and later I call
> the delegate several times. In such situation a delegate is handy to
> shorten my code, where max performance is not needed.
>
> I generally use contract programming, because I've seen it catches some
> of my coding mistakes. So what's
wrong in desiring to add a
> pre-condition to that delegate?

Then it has to be part of the type (a meta-info bound to it)... how would you then check if 2 functions have equivalent (but with different code) preconditions?

 (Currently I have put the pre-condition
> asserts inside the function assigned to the delegate).

Where it truly belongs.

>
> Bye,
> bearophile


-- 
Dmitry Olshansky

Dmitry Olshansky:

> Then it has to be part of the type (a meta-info bound to it)...

In the first case the contracts are shared by all delegates, so there is no need for code equality:

void main() {
    void delegate(int x) foo
    in {
        assert(x > 0);
    };

    foo = (x) {};
}


If the contracts are attached to the function, can't you just trust the programmers to use compatible contracts, so again there's no need to compare code?

void main() {
    void delegate(int) foo;

    foo = (x)
    in {
        assert(x > 0);
    } body {
    };
}


Bye,
bearophile