Call.invoke returns null

On the other hand, it is not hard to implement:. To be honest, we didn't really have to write the new DefaultIfEmpty implementation for this solution to work. Starting with. This is another functional type available in C. It lets us define a delegate which will be invoked only when value is requested for the first time.

There are a couple of changes compared to previous solution. First and most important is that DefaultIfEmpty now receives the lazy string value. Actual value of this string will not be evaluated until its Value property is first time accessed for reading. In other words, the delegate passed to the Lazy constructor is not going to be executed if its result is not going to be used. And we know that it is not going to happen unless Get method of the cache component returned an empty Maybe.

Another difference is the mapping added just after the Get method is executed. This mapping is important because Get method returns collection of strings, while DefaultIfEmpty expects collection of lazy strings. Therefore, we had to convert a string contained in the Maybe object into lazy string before proceeding.

Finally, the last Select call works with the lazy string, rather than the simple string. The change is that, in order to access actual string located inside, we had to read the Value property on the lazy string.

So much about modifications introduced in the solution based on lazy strings. Once again, added overload of the DefaultIfEmpty method is not required anymore and we can freely remove the FunctionalDefaultIfEmpty utility class from the solution. In this article we have tackled the problem of returning null from a method. Several ways to tackle the issue have been presented. More ways exist and can be found in the literature and on the Internet.

Any good solution to the problem will actually make the client code easier to write and to understand. Finally, for your convenience, below is the full source code of the console application which uses the repository and caching component with help of the Maybe class. In this course, you will learn how design patterns can be applied to make code better: flexible, short, readable.

You will learn how to decide when and which pattern to apply by formally analyzing the need to flex around specific axis. This course begins with examination of a realistic application, which is poorly factored and doesn't incorporate design patterns.

It is nearly impossible to maintain and develop this application further, due to its poor structure and design. As demonstration after demonstration will unfold, we will refactor this entire application, fitting many design patterns into place almost without effort. By the end of the course, you will know how code refactoring and design patterns can operate together, and help each other create great design.

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After completing this course, you will know how to develop a large and complex domain model, which you will be able to maintain and extend further. And, not to forget, the model you develop in this way will be correct and free of bugs.

NET technology stack. He can often be found speaking at conferences and user groups, promoting object-oriented and functional development style and clean coding practices and techniques that improve longevity of complex business applications. Toggle navigation Coding Helmet. Articles Exercises Reading List. The Problem of Returning Null In so many occasions we have a method which might not be able to produce its result, given the argument values it received.

Take a look at this example. ContainsKey key return this. Store "a" , "car" ; cache. Store "b" , "truck" ; cache. Store "c" , "bus" ; Console. Remove From My Forums. Answered by:. Archived Forums. Windows PowerShell.

Sign in to vote. Edited by dharric72 Friday, May 4, PM. Friday, May 4, PM. So for whatever reason the call to Invoke causes the hang. I ended up switching to calling a Process object and cmd. Then I avoided waiting for standard out and it works waiting for standard out to finish causes the same issue. Marked as answer by dharric72 Tuesday, May 8, AM.

Priority: Blocker. Resolution: Cannot Reproduce. Labels: None. Thanks in advance. However returning an empty array, , results in null being returned or at least what is stored in the receiving variable.

Let's assume I have no control over what is inside the script block although I could inject code in the beginning of the script block , I just need to act on the return value which could be of any type array, hash table, integer, string, boolean etc. Is there a way from outside the script block to find out if the returned value really was null or?

Attachments: Up to 10 attachments including images can be used with a maximum of 3. The use of "return" in PowerShell is there to break out of a function somewhere other than the end. So, you can see what's happening. PowerShell doesn't just return what follows the 'return', it shoves all uncaptured output into the pipeline.

From a PowerShell prompt, if you were to do this: " " you'd get nothing.