Named and Optional Arguments (C# Programming Guide)

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C 4 introduces named and optional arguments. Named arguments enable you to specify an argument for a particular parameter by associating the argument with the parameter's name rather than with the parameter's position in the parameter list. Optional arguments enable you to omit arguments for some parameters. Both techniques can be used with methods, indexers, constructors, and delegates.

When you use named and out optional parameter c# arguments, the out optional parameter c# are evaluated in the order in which they appear in the argument list, not the parameter list. Named and optional parameters, when used together, enable you to supply arguments for only a few parameters from a list of optional parameters. Named arguments free you from the need to remember or to look up the order of parameters in the parameter lists of called methods. The parameter for each argument can be specified by parameter name.

If you do not remember the order of the parameters but know their names, you can send the arguments in any order. Named arguments also improve the readability of your code by identifying what each argument represents. In the example out optional parameter c# below, the sellerName cannot be null or white space.

As both sellerName and productName are string types, instead of sending arguments by position, it makes sense to use named arguments to disambiguate the two and reduce confusion for anyone reading the code. However, out-of-order named arguments are invalid if they're followed by positional arguments. The definition of a method, constructor, indexer, or delegate can specify that its parameters are required or that they are optional.

Any call must provide out optional parameter c# for all required parameters, but can omit arguments for optional parameters. Each optional parameter has a default value as out optional parameter c# of its definition. If no argument is sent for that parameter, the default value is used.

A default value must be one of the following types of expressions:. Optional parameters are defined at the end of the parameter list, after any required parameters.

If the caller provides an argument for any one of a succession of optional parameters, it must provide arguments for all preceding optional parameters. Comma-separated gaps in the argument list are not supported. For example, in the following code, instance method ExampleMethod is defined with one out optional parameter c# and two optional parameters. The following call to ExampleMethod causes a compiler error, because out optional parameter c# argument is provided for the third parameter but out optional parameter c# for the second.

However, if out optional parameter c# know the name of the third parameter, you can use a named argument to accomplish the task. IntelliSense uses brackets to indicate optional parameters, as shown in the following illustration. Optional parameters in ExampleMethod. You can also declare optional parameters by using the. OptionalAttribute parameters do not require a default value. In the following example, the constructor for ExampleClass has one parameter, which is optional. Instance method ExampleMethod has one required parameter, requiredand two optional parameters, optionalstr and optionalint.

The code in Main out optional parameter c# the different ways in which the constructor and method can be invoked. For example, the AutoFormat method in the Microsoft Office Excel Range interface has seven parameters, all of which are optional. These parameters are shown in the following illustration. However, you can greatly simplify the call to AutoFormat by using named and optional arguments, introduced in C 4.

Named and out optional parameter c# arguments enable you to omit the argument for an optional parameter if you do not want to change the parameter's default value. In the following call, a value is specified for only one of the seven parameters. For more information and examples, see How to: A method, indexer, or constructor is a candidate for execution if each of its parameters either is optional or corresponds, by name or by position, to a single argument in the calling statement, and that argument can be converted to the type of the parameter.

If more out optional parameter c# one candidate is found, overload resolution rules for preferred conversions are applied to the arguments that are explicitly specified. Omitted arguments for optional parameters are ignored. If two candidates are judged to be equally good, preference goes to a candidate that does not have optional parameters for which arguments were omitted in the call.

This is a consequence of a general preference in overload resolution for candidates that have fewer parameters. For more information, see the C Language Specification. Out optional parameter c# language specification is the definitive source for C syntax and usage.

The feedback system for this content will be changing soon. Old comments will not be carried over. If content within a comment thread is important to you, please save a copy. For more information on the upcoming change, we invite you to read our blog post. Named Arguments Named arguments free you from the need to remember or to look up the order of parameters in the parameter lists of called methods.

PrintOrderDetails "Gift Shop", 31, "Red Mug" ; If you do not remember the order of the parameters but know their names, you can send the arguments in any order. Named arguments, when used with positional arguments, are valid as long as they're not followed by any positional arguments, or PrintOrderDetails "Gift Shop", 31, productName: In the example below, the parameter orderNum is in the correct position but isn't explicitly named.

Named argument specifications must appear after all fixed arguments have been specified. A default value must be one of the following types of expressions: ExampleMethod 3, ,4 out optional parameter c# However, if you know the name of the third parameter, you can use a named argument to accomplish the task.

Optional parameters in ExampleMethod Note You can also declare optional parameters by using the. Note The feedback system for this content will be changing soon.

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Last post Mar 22, Mar 18, So, say, we have the following function:. In other words so that the function could be called like so: But in C this doesn't work. Any suggestions how to do the same in C , because I'm missing this functionality a big time? Optional parameters only work with value parameters. It should be noted that C is designed to handle things a little more simply, so it's not that the functionality is missing; it's more like the complexity has been removed.

So, it would appear that you would like to return a list of string items where it could be either one, two, or three items. So, try this instead:.

Coding this way opens up many more possiblities down the chain of parameters. There is another way to do this if you have an unknown amount of parameters you wish to work with. However in all my tests i am seeing that the object is being passed as reference without the ref keyword Take a look at this example below. It passes in a string array, modifies the string array and returns a string value. This is then print to the console try it yourself you will see that my string array is changed in the static method.

Please see the syntax. For more info visit http: I'll keep it in mind though. But again, that is extra work, and it might be easier to simply add a couple of "dummy" variables to pass into optional parameters instead of dedicating time to write whole new methods that don't take them.

Mar 19, Actually, you need to look at the bigger picture. To take advantage of these development platforms, you are mainly limited to C and Visual Basic. However, when it comes to library development, the options are wide open.

NET to use your native Win32 objects within a. NET Framework, though I would suspect that you'll find similar timing issues as what "slows down" C is actually its use of the.

Still, they can both play together within the CLR. But C does not support optional output or reference parameters, which goes to the original question. Ok, having gone back and re-read the original question more closely: It just doesnt make sense.

How can a by-reference parameter have a default value? Just doesnt make semantic sense. The OP is trying to pass reference types, immutable though they may be, like value types. Clearly we have a pointer-semantics vs reference-sematics issue here. You make a good point about the difference between the use of pointers vs. As such, going back to the original question, this clearly shows that the use of output optional parameters are not only inappropriate for C but definitely does not fit in its overall design.

It is not as childish as VB, but it's leaning that way. I also admit that MS dedicated way more resources to their. NET framework than they did to Win32, and it is 10 times easier and faster to code using. But, all that works if you go along the "beaten path", but as soon as you deviate from it, one of those oversimplified languages immediately fails you. That's an exciting statement. By fail, I assume you mean "I don't know how to do something with it, so the language must be broken".

Mar 20, I believe that all you really need to is to use reference parameters:. Did you forget the bit about where the OP stated that he wanted to default the parameters, to which you replied:. The OP wants to default ref parameters by setting them to null. So if the value comes in, then it gets used; if no value comes in then it doesn't. In your code above you force the caller to create the null references, rather than have that nullness defaulted. C provides a solution for this: NET, which is why we mark the code as unsafe.

And this is what I was getting at when I said you seem to be confused about pointer semantics vs reference semantics. C uses references by default notice that you wouldnt have to use dereferencing operator in C. Any two languages can be very different but you get a large productivity boost for that difference if the language is appropriate to the problem.

As for any percieved 'slowness' to the language I'd like to point out that:. Net has a multi-threaded allocator by default. These IO operations are orders of magnitude slower than any slowness you're going to see from the memory allocator or jit compilation.

This keeps stuff much more on the stack thus eliminating the costs of alocating lists which you seemed so averse to earlier. The point of using reference parameters in the first place is that they can be defined prior to call the method the default value and if they are not changed, then the value remains the same in the main calling code.

Note that I am offering an alternative to optional parameters, that is, using reference parameters should provide similar results. I'm certain that the OP knows how to use reference parameters: TryParse is an example of such a need. TryParse to attempt to convert our string s into a valid DateTime and we have provided a variable named "result" FWIW, we are making an implied promise so we had better check the return value to ignore the contents of "result" should the DateTime override fail to convert the string s.

Likewise, a ref parameter will ALWAYS have some initial value because otherwise the c compiler is unlikely to allow you to use it. Similar to the out parameter, a ref parmeter [ http: So if the client passed in a value other than null to strOut1, well tough! Dave, i disagree with your statement " I know what the original poster is asking for, but he cannot have it as expected in C.

Remember that there is a type limitation on what can be used as pointers. Furthermore, I believe that Gerry's solution with the output parameters and then setting the output parameters to their "default" values immediately at the start of the method is a reasonable solution for this problem. I also Gerry's point about pointers: Furthermore, not all languages are suited for what we want to do and this may be one of C 's lines that shouldn't be crossed.

Mar 21, A programming language is a tool that should be used to get the work done for the people paying the money. Shipping working code is paramount in business. Anyone who thinks otherwise must be an academic or consultant. You use the tool effectively to get the job done, and no more. Being precious about features is wrong albeit that I would be challenging pretty hard on major abuses of the language. As an aside, I think that the OP got it wrong when he first wrote out, which hasn't helped.

And your magical initialisation syntax for out parameters makes me want to close my eyes. Please clarify your above statement. I assume you mean this example snippet from http: A Hare Code Monger cranks out code, beats upon it until it appears to work, and delivers it in the most fragile state of existence possible, ready to crumble to dust at the first attempt to modify the code at some future date.

Unenlightened Managers relish Hare Code Mongers because Hare Code Mongers tend to deliver bad but working code on time and under badly forecast budget. Tortoise Code Crafters are thoughtful about their code, likely to use TDD appropriately, unlikely to abuse their programming language, do not always meet the expectations of the Unenlightened Managers, likely to miss unrealistic deadlines, yet tend to deliver robust code that is less expensive and more maintainable over the life span of their creations.

Sadly, imho, in our profession Hare Code Mongers substantiantially outnumber Tortoise Code Crafters; likewise there exists legions of Unenlightened Managers for every Enlightened Manager imprisoned by mediocrity.

And this is the problem. The real issue isnt that there isnt a way to achieve what the OP wants, its that the OP has decided against the more standard ways of solving the problem.

The question was not phrased in terms of "I've got code that has to work this way " it was phrased in terms of:. In this case the given example just doesnt match the semantics your average. Net programmer would expect. While it might be good intellectual excercise for four posters with "All-Star" ratings to debate, I doubt it's going to help the OP learn not just the language but the conventions for C. The code shown would not pass a code-review with me. In this case, because the OP is still learning, the most correct answer is the answer that would pass a code review.

Jeffrey, a debate tends to become a contest where there's one winner Jeffrey, are you referring to the O. This has nothing whatsoever to do with experienced and skilled developers making pragmatic design tradeoffs. You need to start getting agile, and flexible, if you want to code into the future. I guess you learned traditional BDUF, and have a hard time working in a more dynamic way.

A decent developer knows when, and where, to push the boundaries.