Learning Swift from scratch (Day54)-throwing errors

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A function or method that can be placed behind a try is required, and they are likely to throw an error, which is appended with the throws keyword after the arguments to the function or method declaration, indicating that the function or method can throw an error.

The example code for declaring a throw error method is as follows:

// Delete Note Recording method func Remove (model:note) throws {  ...} // querying all record data methods  -- [Note] {    ...}

The above code remove (_:) method has no return value, and the throws keyword is placed after the parameter. FindAll () has a return value of throws keyword placed between the parameter and the return value type.

Throw an error in a function or method

A function or method can declare a throw error because an error is generated and thrown in a function or method, so that a function or method declaration throws an error in practical sense.

In generating and throwing the wrong way:

L artificially throws an error in a function or method through a throw statement.

Other functions or methods that are called in a function or method can throw an error function or method, but no catch processing can cause errors to be propagated.

The sample code is as follows:

//Delete Note Methodfunc Remove (model:note)throws{Guard Let date= Model.dateElse{//when the judgment is thrown, there is a guard statement.//throw "PRIMARY key is empty" error        ThrowDaoerror.primarykeynull}//Compare date primary keys are equal     for(index, note) in Listdata.enumerate () where note.date = =Date {listdata.removeatindex (index)}}//querying all data methodsfunc findAll ()throws-[Note] {guard Listdata.count> 0Else{//when the judgment is thrown, there is a guard statement.//throws "no data" error.         ThrowDaoerror.nodata}returnlistdata}func printnotes ()throws{//declaration throws an errorLet datas=TryfindAll () forNote in datas {print ("Date: \ (note.date!) -Content: \ (note.content!) ")    }}TryPrintNotes ()

The Guard statement is best at dealing with this early judgment, which throws an error when the condition is false.

The FINDALL () statement itself is likely to produce an error, but it is not captured and processed using a catch statement, which causes the error to propagate to the caller of the function or method, and if neither of its callers captures processing, the last program will have a run-time error.

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Learning Swift from scratch (Day54)-throwing errors