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