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Comment by AaronFriel | Hacker News Reader

Oh, today I learned. I think this was an issue in Scala (with `var`), but this seems like a great compromise for Java core.

I suppose Java had many years after C#'s introduction of closures to reflect on what went well and what did not. Go, created in 2007, predates both languages having lightweight closures. Not surprising that they made the decision they did.

Your comment inspired me to ask what Rust does in this situation, but of course, they've opted for both a different "for" loop construct, but even if they hadn't, the borrow checker enforces a similar requirement as Java's effectively final lambda limitation.

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Newcomers to Java usually dislike the "Variable used in lambda expression should be final or effectively final" compiler error, but once you understand why that restriction is in place and what happens in other languages when there's no such restriction, you start to love the subtle genius in how Java did it this way.

Go, designed between 2007 and 2009, certainly had the opportunity to look at their introduction in C# 2.0, released 2005, or its syntactic sugar added in C# 3.0, released 2007.

I think that's an ahistorical reading of events. They did have the opportunity, but there were very few languages doing what Go was at the time it was designed. My recollection of the C# 3 to 5 and .NET 3 to 4.5 is a bit muddled, but it looks like the spec supports a different reading:

C# 3.0 in 2007 introduced arrow syntax. I believe this was primarily to support LINQ, and so users were typically creating closures as arguments to IEnumerable methods, not in a loop.

C# 4.0 in 2010 introduced Task<T> (by virtue of .NET 4), and with this it became much more likely users would create a closure in a loop. That's how users would add tasks to the task pool, after all, from a for loop.

C# 5.0 in 2012 fixes loop variable behavior.

I think the thesis I have is sound: language designers did not predict how loops and lightweight closures would interact to create error-prone code until (by and large) users encountered these issues.

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