C#•2y ago

❔ what is difference between _ and ()?

I have following in constuctor:

var initialize = ReactiveCommand.CreateFromTask( async () =>                     
 {                                                                                
     const string databaseFileName = "log.db";                                    
     var databaseFilePath = Path.Combine( Path.GetTempPath(), databaseFileName ); 
     var database = new SQLiteAsyncConnection(databaseFilePath);                  
                                                                                  
     await database.CreateTableAsync<MqttDelivery>();                             
 } );                                                                             
 initialize.Subscribe();                                                          
 initialize.Execute();                                                            

 var initialize = ReactiveCommand.CreateFromTask( async _ =>                     
 {                                                                                
     const string databaseFileName = "log.db";                                    
     var databaseFilePath = Path.Combine( Path.GetTempPath(), databaseFileName ); 
     var database = new SQLiteAsyncConnection(databaseFilePath);                  
                                                                                  
     await database.CreateTableAsync<MqttDelivery>();                             
 } );                                                                             
 initialize.Subscribe();                                                          
 initialize.Execute();

var initialize = ReactiveCommand.CreateFromTask( async () =>                     
 {                                                                                
     const string databaseFileName = "log.db";                                    
     var databaseFilePath = Path.Combine( Path.GetTempPath(), databaseFileName ); 
     var database = new SQLiteAsyncConnection(databaseFilePath);                  
                                                                                  
     await database.CreateTableAsync<MqttDelivery>();                             
 } );                                                                             
 initialize.Subscribe();                                                          
 initialize.Execute();                                                            

 var initialize = ReactiveCommand.CreateFromTask( async _ =>                     
 {                                                                                
     const string databaseFileName = "log.db";                                    
     var databaseFilePath = Path.Combine( Path.GetTempPath(), databaseFileName ); 
     var database = new SQLiteAsyncConnection(databaseFilePath);                  
                                                                                  
     await database.CreateTableAsync<MqttDelivery>();                             
 } );                                                                             
 initialize.Subscribe();                                                          
 initialize.Execute();

the first one will be executed second one will be skipped why?

5 Replies

SWEETPONYOP•2y ago

hm, second one will be called if I call command again interesting! It doesn't run in constructor but it can be runned directly ah okay! thanks

Angius•2y ago

_ is a discard So () => foo is a parameterless lambda While _ => foo is a lambda with one parameter, but you don't need it so you discard it Similarly, (_, _) => foo is a lambda with two params, both discarded Etc

SWEETPONYOP•2y ago

thats why task wouldn't be executed in constructor?

Angius•2y ago

Seeing how the version with a parameter is supposed to get a cancellation token, and it gets discarded instead... possibly

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ what is difference between _ and ()?