Interpret c# lambda syntax

Question

I have a general understanding of Lambda expressions but not sure what the () => syntax means. This code appears to return a list of Task items but I'm unsure how it executes or how to interpret what it means.

Can someone tell me:

what does () => mean?
It appears that each of the new Task blocks are executed sequentially?

 private DateTime? _myTime = null;
 private DateTime? _theirTime = null;
 private bool _okToProcess = true;

 List<Task> myTasks = new List<Task>
            {
                   new Task( () => 
                    {
                        _myTime = GetMyTime();
                    }),

                     new Task( () => 
                    {
                        _theirTime = GetTheirTime(); 
                        _okToProcess = _myTime > _theirTime;                                         
                    }),

                new Task(() => 
                    {
                        if (_okToProcess)
                        {
                           WriteToMyLogStep("We are processing");
                        }
                        else
                        {
                           WriteToMyLogStep("We are NOT processing");
                        }
                     });
            };

1: the action to be executed; 2: the tasks are only defined, not executed. — Alex Filipovici
– Alex Filipovici, Commented Feb 22, 2013 at 16:37
You shouldn't ask two distinct questions at the same time. Next time, actually post two different questions. — svick
– svick, Commented Feb 22, 2013 at 16:59

Freeman · Accepted Answer · 2013-02-22 16:42:44Z

4

() - represents the parameters taken by the anonymus method,

=> - is generally read goes to and points to the anonymus methods body that uses those parameters (if any provided).

In your case the lamda expression is the same as:

 delegate() {  _myTime = GetMyTime(); }

As for the Tasks they are just added to a list, they are not executed. How they will be executed depends on how you want to execute them in the future. (maybe in a loop on the same thread or maybe on different threads).

edited Feb 22, 2013 at 16:42

answered Feb 22, 2013 at 16:36

Freeman

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3 Comments

svick Over a year ago

I'm not sure if explaining lambdas using the old delegate syntax (which is not used much) is helpful.

Freeman Over a year ago

well, old delegate syntax resembles more to a normal method compared to lambdas, thus you can get a better picture. I'm talking from an unexperienced point of view. wouldn't you agree?

MikieIkie Over a year ago

Great answer Freeman!... and this helped me to better understand this syntax and put things in perspect. Thanks

Brian Rasmussen · Accepted Answer · 2013-02-22 16:37:38Z

4

The () => syntax just means that there's no named input to the lambda. It is like calling a method that takes no parameters.

As for the code the tasks are just created but never actually started, so they don't run in the code shown. I assume the list is enumerated and the tasks started somewhere else.

answered Feb 22, 2013 at 16:37

Brian Rasmussen

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1 Comment

MikieIkie Over a year ago

Thanks @BrianRasmussen. Each task IS executed using the Start method later in the code thru an enumeration of the list.

Bobson · Accepted Answer · 2013-02-22 16:38:58Z

2

You're probably used to seeing lambda functions like x => DoSomething(x). That's actually shorthand for (x) => DoSomething(x) - the initial (x) represents the parameters to the function, the same as the (x) in DoSomething(x). does.

In this case, there are no parameters, so it uses (), the same as a regular function would be DoSomething().

As for the Tasks, they'll run in parallel once started, unless you explicitly wait until each one is done before starting the next.

answered Feb 22, 2013 at 16:38

Bobson

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1 Comment

MikieIkie Over a year ago

thx for the clarification... (the Tasks) "they'll run in parallel once started, unless you explicitly wait until each one is done". Correct, each task is started in an enumeration like: task.Start; task.Wait();

Twiltie · Accepted Answer · 2013-02-22 16:38:04Z

0

() would be similar to the parameters the function takes, and I believe that tasks are executed asynchronously => Points to the body of the function

answered Feb 22, 2013 at 16:38

Twiltie

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Comments

Alex Filipovici · Accepted Answer · 2013-02-22 16:38:51Z

0

The anonymous Action to be executed;
The tasks are only defined, not executed.

answered Feb 22, 2013 at 16:38

Alex Filipovici

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Comments

Lawrence Wagerfield · Accepted Answer · 2013-02-22 16:39:02Z

0

()=> is an Action - an expression with no parameters.

These tasks have not been started so (currently) will never complete...

answered Feb 22, 2013 at 16:39

Lawrence Wagerfield

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Comments

svick · Accepted Answer · 2013-02-22 16:58:36Z

0

() is your list of parameters, in your case empty or none, that is getting passed into the anonymous function following the => operator. The => gets its name from Lambda calculus.
It depends on how you are calling your tasks in the list. This is simply a List<Task> with Tasks in it. In order to execute your tasks you would need to do something like this:
```
foreach (Task t in myTasks) {
    t.RunSynchronously();  // in this case the tasks would run synchronously
}
```

edited Feb 22, 2013 at 16:58

svick

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answered Feb 22, 2013 at 16:39

Ian R. O'Brien

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