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I tried to catch an Exception but the compiler gives warning: This type test or downcast will always hold
let testFail () =
try
printfn "Ready for failing..."
failwith "Fails"
with
| :? System.ArgumentException -> ()
| :? System.Exception -> ()
The question is: how to I do it without the warning? (I believe there must be a way to do this, otherwise there should be no warning)
Like C#
try
{
Console.WriteLine("Ready for failing...");
throw new Exception("Fails");
}
catch (Exception)
{
}
338
If you catch System. Exception , rethrow it using the throw keyword at the end of the catch block. If a catch block defines an exception variable, you can use it to obtain more information about the type of exception that occurred. Exceptions can be explicitly generated by a program by using the throw keyword.
Another way to catch all Python exceptions when it occurs during runtime is to use the raise keyword. It is a manual process wherein you can optionally pass values to the exception to clarify the reason why it was raised. if x <= 0: raise ValueError(“It is not a positive number!”)
Exception handling is used to handle the exceptions. We can use try catch block to protect the code. Catch block is used to catch all types of exception. The keyword “catch” is used to catch exceptions.
Catching Specific Exceptions in Python A try clause can have any number of except clauses to handle different exceptions, however, only one will be executed in case an exception occurs. We can use a tuple of values to specify multiple exceptions in an except clause.
C#:
void testFail()
{
try
{
Console.WriteLine("Ready for failing...");
throw new Exception("Fails");
}
catch (ArgumentException)
{
}
catch
{
}
}
F# equivalent:
let testFail () =
try
printfn "Ready for failing..."
failwith "Fails"
with
| :? System.ArgumentException -> ()
| _ -> ()
C#:
void testFail()
{
try
{
Console.WriteLine("Ready for failing...");
throw new Exception("Fails");
}
catch (ArgumentException ex)
{
}
catch (Exception ex)
{
}
}
F# equivalent:
let testFail () =
try
printfn "Ready for failing..."
failwith "Fails"
with
| :? System.ArgumentException as ex -> ()
| ex -> ()
C#:
void testFail()
{
try
{
Console.WriteLine("Ready for failing...");
throw new Exception("Fails");
}
catch
{
}
}
F# equivalent:
let testFail () =
try
printfn "Ready for failing..."
failwith "Fails"
with
| _ -> ()
As Joel noted, you would not want to use catch (Exception) in C# for the same reason you don't use | :? System.Exception -> in F#.
118
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