Hacker News Reader

Comment by skrebbel | Hacker News Reader

I'm very happy to see that contracts play such a central role in this language. I hope that this will mean that contracts will finally gain more popularity, if Microsoft manages to push this language well enough.

I feel that 70% of what I write in unit tests and ifs-at-the-start-of-a-method should be in contracts, and the only reason they're expressed so cumbersome is because the languages I use don't support any better.

View on HN

ifs-at-the-start-of-a-method

Even for a simple if: DRY! You should have put those in reusable functions with nice understandable names ages ago :]

do you know what contracts are?

Typical contracts are 'assert (arg != null)' or 'assert(arg1.length == arg2.length)' or 'assert (hour >= 0 and hour <= 23)'

yes I know what they are. Use them all the time. But since the post is about if I imagine it's about things like

  if( x < 0 || x > 5 )
    throw new ArgumentOutOfRange();
  if( y == nullptr )
    thwrow new NullRefException();

which should imo be something like

  Contract.AssertInRange( x, 0, 5 );
  Contract.AssertNotNull( y );

It is possible to write your own contract abbreviators with Code Contracts so I would hope such functionality gets added to the new language. The post does mention however that object invariants are not supported so I do wonder how much Code Contracts are actually influencing it.

I imagine you could do even better with something like PostSharp or Fody.

    public void MyFunction([InRange(0, 5)] int x, [NotNull] object y)
    {
        // ...
    }

I just checked, and in fact Fody can do something just like this [1].

The only downside I see is contracts like this would be hard to write concisely:

    if (useFirstObject == true)
        Contract.AssertNotNull(firstObject);
    else
        Contract.AssertNotNull(secondObject);

[1] https://github.com/Fody/NullGuard

Reply on news.ycombinator.com