Try.md

Try

This represents the Try (or Exceptional) monad.

Construction and Binding

The Try monad allows for defining a chain of lazily executed operations that are executed sequentially. In case of exceptions, the next appropriate (i. e. assignment compatible) catch handler will be invoked. The whole Tryconstruction and execution is primarily regarded an expression, this means every catch-handler must return a value.

Try<int> tryResult = Try
    .Do(_SomeMethod)
    .Then(_SomeOtherMethodThatThrows)
    .Then(_AndAnotherMethod) // assuming _AndAnotherMethod() returns an int
    .Catch<InvalidOperationException>(ex => 
    {
        Log.WriteError("Operation did not succeed");
        return -99;
    });

The constructed tryResult will not be executed until Execute() is invoked on it.

int result = tryResult.Execute();

If no apropriate catch-handler is found, execution of the Try throws:

var result = Try
    .Do<int>(() => throw new ArithmeticException())
    .Catch<InvalidOperationException>(ex => 
    {
        Log.WriteError("Operation did not succeed");
        return -99;
    })
    .Execute(); // throws an ArithmeticException

Execution of an empty Try<T> or TryAsync<T> leads to default(T):

var result = default(Try<string>).Execute(); 
// result is default(string)

Async/Await Support

There is an async variant for all construction and binding methods.

var result = await Try
    .DoAsync(_SomeAsyncMethod)
    .ThenAsync(_SomeOtherAsyncMethodThatThrows)
    .ThenAsync(_AndAnotherAsyncMethod)
    .CatchAsync<InvalidOperationException>(async ex => 
    {
        Log.WriteError("Operation did not succeed");
        return -99;
    })
    .ExecuteAsync();

The explicit calls to .Execute() and .ExecuteAsync() can be 'replaced' by an await because both Try`1 and AsyncTry`1 are awaitables:

var result = await Try
    .DoAsync(_SomeAsyncMethod)
    .ThenAsync(_SomeOtherAsyncMethodThatThrows)
    .ThenAsync(_AndAnotherAsyncMethod)
    .CatchAsync<InvalidOperationException>(async ex =>
    {
        Log.WriteError("Operation did not succeed");
        return -99;
    });

Infrastructure Methods

All .Catch<T>(..) and .CatchAsync<T>(..) variants also provide overloads that allow for specifying the exception type as Type object.

var result = await Try
    .DoAsync(_SomeAsyncMethod)
    .CatchAsync(
        typeof(InvalidOperationException),
        async ex =>
        {
            Log.WriteError("Operation did not succeed");
            return -99;
        });