C# try-catch-else

Question

One thing that has bugged me with exception handling coming from Python to C# is that in C# there doesn\'t appear to be any way of specifying an else clause. For example, in

Answer 1

There might not be any native support for try { ... } catch { ... } else { ... } in C#, but if you are willing to shoulder the overhead of using a workaround, then the example shown below might be appealing:

using System;

public class Test
{
    public static void Main()
    {
        Example("ksEE5A.exe");
    }

    public static char Example(string path) {
        var reader = default(System.IO.StreamReader);
        var line = default(string);
        var character = default(char);
        TryElse(
            delegate {
                Console.WriteLine("Trying to open StreamReader ...");
                reader = new System.IO.StreamReader(path);
            },
            delegate {
                Console.WriteLine("Success!");
                line = reader.ReadLine();
                character = line[30];
            },
            null,
            new Case(typeof(NullReferenceException), error => {
                Console.WriteLine("Something was null and should not have been.");
                Console.WriteLine("The line variable could not cause this error.");
            }),
            new Case(typeof(System.IO.FileNotFoundException), error => {
                Console.WriteLine("File could not be found:");
                Console.WriteLine(path);
            }),
            new Case(typeof(Exception), error => {
                Console.WriteLine("There was an error:");
                Console.WriteLine(error);
            }));
        return character;
    }

    public static void TryElse(Action pyTry, Action pyElse, Action pyFinally, params Case[] pyExcept) {
        if (pyElse != null && pyExcept.Length < 1) {
            throw new ArgumentException(@"there must be exception handlers if else is specified", nameof(pyExcept));
        }
        var doElse = false;
        var savedError = default(Exception);
        try {
            try {
                pyTry();
                doElse = true;
            } catch (Exception error) {
                savedError = error;
                foreach (var handler in pyExcept) {
                    if (handler.IsMatch(error)) {
                        handler.Process(error);
                        savedError = null;
                        break;
                    }
                }
            }
            if (doElse) {
                pyElse();
            }
        } catch (Exception error) {
            savedError = error;
        }
        pyFinally?.Invoke();
        if (savedError != null) {
            throw savedError;
        }
    }
}

public class Case {
    private Type ExceptionType { get; }
    public Action Process { get; }
    private Func When { get; }

    public Case(Type exceptionType, Action handler, Func when = null) {
        if (!typeof(Exception).IsAssignableFrom(exceptionType)) {
            throw new ArgumentException(@"exceptionType must be a type of exception", nameof(exceptionType));
        }
        this.ExceptionType = exceptionType;
        this.Process = handler;
        this.When = when;
    }

    public bool IsMatch(Exception error) {
        return this.ExceptionType.IsInstanceOfType(error) && (this.When?.Invoke(error) ?? true);
    }
}