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I love closures and lambdas, but I was quite amused when I wrote the following buggy code:
for (int i=0; i <= 10; i++)
{
var task = Task.Run(async () =>
{
var convertResp = await StartTestConvert(i);
... other stuff
});
} And was wondering, how in the world does i get equal to 11!!!
Answer: bad closure. Fix:
for (int i=0; i <= 10; i++)
{
int n = i;
var task = Task.Run(async () =>
{
var convertResp = await StartTestConvert(n);
... other stuff
});
}
I think this would make a good interview question!
modified 4-Mar-24 10:13am.
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Marc Clifton wrote: I think this would make a good interview question!
And I thought this was fairly common knowledge!
(Not that that would preclude it from being an interview question, of course.)
They "fixed" the behaviour for the foreach loop back in C# 5, but deliberately chose not to change the for loop:
UPDATE: We are taking the breaking change. In C# 5, the loop variable of a foreach will be logically inside the loop, and therefore closures will close over a fresh copy of the variable each time. The for loop will not be changed.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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That's the follow-up interview question. "On what for loops does closure work?"
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From my experience there are most probably programmers who would fix it like this
for (int i = 0; i <= 10; System.Threading.Thread.Sleep(10), i++)
{
....
}
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Reminded me of The Deadlock Empire[^].
A game where you're a scheduler and have to break code by switching contexts
You can play it for free in your browser, no registration or anything.
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I do not see the difference whether using i or n.
Is async call creating a thread?
Is this a C# thing?
lambda?
Closure? seems like a definition of global and local variable spaces.
Confused
"A little time, a little trouble, your better day"
Badfinger
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It has to do with capture, where we grab the value of i by the use of assignment into n before launching another task.
There is nothing magical about using a variable named n ... we could have called it george . What's important is that the current value of i in the for loop is captured before launching the task.
If we had not done that, the for loop would complete execution, setting i to 11 before the first task was launched. That is what is meant by closure.
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Marc Clifton wrote: I think this would make a good interview question! To mention the language that shall not be named (it rhymes with GuavaScript), closures was one of the ways to fake OOP before es6 came along with classes.
function FakeClass() {
const protectMe = 'When I grow up, I wanna be a class!';
this.doSomething = function() {
console.log(protectMe);
}
}
const sup = new FakeClass();
console.log(sup.protectMe);
sup.doSomething();
These days I tend to use closures less and less with generators, promises, async/await, etc. There are just new ways to do the same thing in the language that shall not name be named. But, if you ever find yourself needing to access that lexical context after the parent function go bye bye (a static variable wouldn't quite cut it for that) and you don't want to clutter up your code with global/module crap... closures are a life saver.
All-in-all, cool stuff.
Jeremy Falcon
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lambdas/closures are used in "Lisp, C#, C++, Lua, Python, Ruby, JavaScript, Java, Excel or Google sheets" according to stack overflow, hence my unfamiliarity, being a lowly C guy. Thanx to CP, I have a new appreciation.
"A little time, a little trouble, your better day"
Badfinger
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C’s still an awesome language. Always will be. Can’t hurt to learn a second one though to be introduced to modern concepts. Some you can bring back to C, even if you have to implement them yourself. Either way, C rulez yo.
Jeremy Falcon
modified 5-Mar-24 9:15am.
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thanx jeremy this helps
"A little time, a little trouble, your better day"
Badfinger
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You’re welcome man. You can actually do even more with closures too. Might type up some other examples tomorrow.
Jeremy Falcon
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That is why Java will only let you use final “variables” for anonymous inner classes.
Does StartTestConvert() receive by value/copy or by reference? ( Does it matter?)
I would tend to wrap some of this into a class. I have moved in the direction of hiding threads/locks/async/await etc as much as possible from the client code.
new Runner(i).launch();
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int n = i;
Amazing solution from an amazing language to cut the code clutter delivered to you by the Cool Kids on the Codeblock!
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From the good, old K&R C bible:
A for that does not include a continue:
for (e1; e2; e3)
Block;
is equivalent to:
e1;
while(e2)
{
Block;
e3;
}
Replace e1 with (int i = 0;) and it will become clear what is the scope of i, and why it will have value 11.
All subsequent languages like C++, java, C# etc. follows the same logic, since nobody dares to change what DMR (may God rest his soul in peace) has ruled.
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ChatGPT explained this to me. I feel bad that I couldn't figure this one out
Question to ChatGPT:
In this example c# code "i" can equal 11. can you fix it?
for (int i=0; i <= 10; i++)
{
var task = Task.Run(async () =>
{
var convertResp = await StartTestConvert(i);
... other stuff
});
}
Response:
Yes, in the provided code, the variable i is captured by the async lambda expression, which means by the time the async operations inside the lambda complete, the value of i may have changed. To fix this, you need to capture the loop variable correctly. Here's a way to do it:
for (int i = 0; i <= 10; i++)
{
int current = i;
var task = Task.Run(async () =>
{
var convertResp = await StartTestConvert(current);
});
}
By capturing the loop variable inside the loop, you ensure that each async operation receives its own copy of the loop variable, preventing the issue where the value of i changes before the async operation completes.
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I just had a conversation with ChatGPT about the topic. It was interesting that I was asking it questions about some specifics about what it was explaining and it did not fall over into a "I'm sorry, 2 plus 2 does equal 5" type of conversation. That has happened a lot to me in the past when trying to understand something.
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I will continue to utilize my logitech but perhaps some here will find this useful.
Coolest mouse ever[^]
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I'm not sure about the 'coolest' part... probably there is some heat involved...
"If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization." ― Gerald Weinberg
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I wonder who will be the first.
GCS/GE d--(d) s-/+ a C+++ U+++ P-- L+@ E-- W+++ N+ o+ K- w+++ O? M-- V? PS+ PE Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- r+++ y+++* Weapons extension: ma- k++ F+2 X
The shortest horror story: On Error Resume Next
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I have to imagine it somehow has the smarts to know when your finger is leaving your desk so for example you scratch an itch, or start typing, or write something down on a piece of paper. Otherwise the pointer constantly trying to follow you will get really annoying, really fast.
Especially if the solution is to temporarily take it off.
Hard to tell from 17-second video (preceeded by two unskippable 15-second ads, thanks YouTube).
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dandy72 wrote: preceeded by two unskippable 15-second ads, thanks YouTube
Isn't it fascinating that the company chooses to host the video on YouTube instead on its own web server? Like they try to monetize their own ads (not really)...
(I use FF with uBlock Origin - no YouTube ads)
"If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization." ― Gerald Weinberg
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one of the co-founders here. Besides other sensors, the ring has also a camera and an 8-core parallel processor. So it recognizes different situations and objects like a keyboard and pauses. When your hand goes back to the desk, the 'mouse' works immediately. If you want to make sure it's off, just rotate your hand accordingly.
Will post soon more videos of our currently running preview sessions where people experience these things first hand.
Sorry about the ads, we cannot disable them on YouTube. You are right, we will need a better solution.
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mspad wrote: a camera and an 8-core parallel processor
In a standard, finger-sized ring? Is that overkill, or necessary? How hot does it get? And I would imagine it needs a battery.
Either way...color me intrigued, I'm definitely keeping an eye out for this.
Has anyone thought about what might be possible with multiple rings working together?
And...scrollwheels are now a must for me. Any emulation for that? I would imagine the most natural thing would be to make up/down gestures with the middle finger.
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