CODEWITHSUNDEEP
c#lambda
user1523271
user1523271

Reputation: 1063

How is lambda parameter inferred?

This is sample code from Microsoft, explaining how chaining tasks works:

using System;
using System.Threading.Tasks;

1.    public class Example
2.    {
3.       public static async Task Main()
4.       {
5.          // Execute the antecedent.
6.          Task<DayOfWeek> taskA = Task.Run( () => DateTime.Today.DayOfWeek );
7.         // Execute the continuation when the antecedent finishes.
8.          await taskA.ContinueWith
9.               ( antecedent => Console.WriteLine("Today is {0}.", antecedent.Result) );
10.       }
11.    }

On line #9 ContinueWith is passed a lambda expression.

My question is: how does the compiler know what antecedent is and where to take it from? I mean, taskA has a Result property and can be passes as an argument, but does the compiler just go around the code and when it sees the first thing that can be passed it picks it?

Upvotes: 0

Views: 73

Answers (2)

NetMage
NetMage

Reputation: 26917

Lambda parameter inference matches the parameter antecedent to the Task<DayOfWeek>.ContinueWith(Action<System.Threading.Tasks.Task<DayOfWeek>> continuationAction) continuationAction parameter, and so sets the type of antecedent to Task<DayOfWeek>.

ContinueWith passes the completed Task<DayOfWeek> taskA as the parameter to the lambda because that is what it is defined to do: see the documentation.

Upvotes: 0

Aleš Doganoc
Aleš Doganoc

Reputation: 12052

The Task ContinueWith method has specific overloads that define what kind of function it accepts as the parameter which defines the function parameters. You have a lot of options so check the official documentation for details.

The sample uses the ContinueWith(Action<Task<TResult>>) the most basic overload where you can see the parameter is specified in the method definition this is how the Action parameter type is defined. You call ContinueWith on a Task<DayOfWeek> so the TResult type is DayOfWeek and the methods signature inferred looks then like this ContinueWith(Action<Task<DayOfWeek>>) for this case.

Upvotes: 2

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