Re: Contracts inheritance

[Ali Çehreli]

On 04/13/2012 03:07 PM, Eyyub wrote:
Hai,
After watching Walter's video at Lang.NEXT, I have wanted to know how
contracts inheritance works.

In the following code, I don't understand why foo.bar(2) works...but
with the sames contracts in the foo function it doesn't work.

http://paste.pocoo.org/show/3Ab5IiQk6hTiJ0jAFZWv/

Thanks

Here is the for convenience:

import std.stdio;

interface IFoo
{
        void bar(int a)
        in
        {
                assert(a != 1);
        }
}

class Foo : IFoo
{
        this()
        {}
        
        override void bar(int a)
        in
        {
                assert(a != 2);
        }
        body
        {
                writeln(a); // 2
        }
}

void foo(int a)
in
{
                assert(a == 2);
                assert(a < 2);
}
body
{
        writeln(a);
}
                
                
void main()
{
        foo(2); // don't pass
        Foo foo2 = new Foo;
        foo2.bar(2); // pass
}

foo(2) cannot work because of the second assert in the 'in' contract.

foo2.bar(2) passes because passing a single 'in' contract is sufficient. 
The 'in' contract of IFoo.bar() requires that a != 1 and it is satisfied 
for 2 so bar() can be called with argument 2.

Ali