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Comment by MatthewPhillips | Hacker News Reader

C# has closures but not when evented. That's the problem with these Language X to js projects. No language is really like JavaScript. Except CoffeeScript, of course. I'm sure you can write clean C# dom code but it won't be like js or like Silverlight. It will need new patterns.

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As someone writing a compiler which targets Javascript, I'm curious: what exactly is the problem you are referring to?

No language is really like x86 machine code, either, but that doesn't seem to have stopped people from writing anything-to-x86 compilers.

What? C# has closures but the CLR doesn't. For the CLR, it's just yet another object of some class, where the class has a relatively funky name.

True about the new patterns, btw. I guess you'd need to port a jQuery to .NET first in order to be productive.

C# has closures but not when evented.

What does this mean? How do closures behave any differently when a delegate is assigned as an event handler?

    var outer = 2;
    var btn = new Button()
    {
        Text = "Click Me"
    };
    btn.Click += (obj, eventArgs) =>
    {
        var local = outer + outer;
    };

How is the above any different/better/worse than what javascript can do?

I reserve the right to be wrong here, but I'm pretty sure in your example outer will be be null on the onclick.

Outer is (implicitly) typed as an int, so it cannot be null under any circumstances. The default value for ints is 0. However, outer will be 2 in this case. Environment capture makes it do what it looks like, just like javascript.

I don't know what you mean by "has closures but not when evented."

If outer were anything but 2 in the click handler, it wouldn't be a closure, which by definition closes over its environment.

outer will be 2

A closure is created for the anonymous function, allowing access (by reference) to the non-local variables in the containing method.

Ok I tested it and you have access to outer here. I must be thinking of something else. Asynchronous web requests?

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