Named arguments also improve the readability of your code by identifying what each argument represents. In the example method below, the sellerName can't 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.
The definition of a method, constructor, indexer, or delegate can specify its parameters are required or optional. Any call must provide arguments for all required parameters, but can omit arguments for optional parameters.
Each optional parameter has a default value as part 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 aren't supported. For example, in the following code, instance method ExampleMethod is defined with one required and two optional parameters.
In the following example, the constructor for ExampleClass has one parameter, which is optional. Instance method ExampleMethod has one required parameter, required, and two optional parameters, optionalstr and optionalint. The code in Main shows the different ways in which the constructor and method can be invoked.
However, you can greatly simplify the call to AutoFormat by using named and optional arguments. Named and optional arguments enable you to omit the argument for an optional parameter if you don't want to change the parameter's default value. In the following call, a value is specified for only one of the seven parameters.
Edit: I know that at the time the question was asked, C# 4.0 didn't exist. But this question still ranks #1 in Google for "C# optional arguments" so I thought - this answer worth being here. Sorry.
UPDATE: This mentioned above WAS the way that I did default values with C# 2.0. The projects I'm working on now are using C# 4.0 which now directly supports optional parameters. Here is an example I just used in my own code:
In our API wrapper, we detect optional parameters (ParameterInfo p.IsOptional) and set a default value. The goal is to mark parameters as optional without resorting to kludges like having "optional" in the parameter name.
When you define a method that way you have the freedom to set just the parameters you want by naming them. See the following link for more information on named and optional parameters:
I agree with stephenbayer. But since it is a webservice, it is easier for end-user to use just one form of the webmethod, than using multiple versions of the same method. I think in this situation Nullable Types are perfect for optional parameters.
The typical way this is handled in C# as stephen mentioned is to overload the method. By creating multiple versions of the method with different parameters you effectively create optional parameters. In the forms with fewer parameters you would typically call the form of the method with all of the parameters setting your default values in the call to that method.
For a larger number of optional parameters, a single parameter of Dictionary could be used with the ContainsKey method. I like this approach because it allows me to pass a List or a T individually without having to create a whole other method (nice if parameters are to be used as filters, for example).
A little late to the party, but I was looking for the answer to this question and ultimately figured out yet another way to do this. Declare the data types for the optional args of your web method to be type XmlNode. If the optional arg is omitted this will be set to null, and if it's present you can get is string value by calling arg.Value, i.e.,
I have a web service to write that takes 7 parameters. Each is an optional query attribute to a sql statement wrapped by this web service. So two workarounds to non-optional params come to mind... both pretty poor:
I had to do this in a VB.Net 2.0 Web Service. I ended up specifying the parameters as strings, then converting them to whatever I needed. An optional parameter was specified with an empty string. Not the cleanest solution, but it worked. Just be careful that you catch all the exceptions that can occur.
optional parameters are nothing but default parameters!i suggest you give both of them default parameters.GetFooBar(int a=0, int b=0) if you don't have any overloaded method, will result in a=0, b=0 if you don't pass any values,if you pass 1 value, will result in, passed value for a, 0 and if you pass 2 values 1st will be assigned to a and second to b.
In the case when default values aren't available the way to add an optional parameter is to use .NET OptionalAttribute class - -us/dotnet/api/system.runtime.interopservices.optionalattribute?view=netframework-4.8
This is called as named arguments. Several others languages provide this feature, and it's common form them to use the syntax foo(5, optionalZ=8) instead, which is useful to know when reading code in other languages.
Another dynamic way to supply parameters of your choise is to implement your method(s) in a class and supply named parameters to the class constructor. Why not even add calls to methods on same line of code as mentioned here : How to define named Parameters C#
Microsoft introduced support for named and optional parameters in C# 4.0. While a named parameter is used to specify an argument based on the name of the argument and not the position, an optional parameter can be used to omit one or more parameters in the method signature. The parameters of a method can be either required or optional depending on whether or not you need to pass a value to these parameters when the method is called.
It should be noted that named and optional parameters can be used not only with methods but also with indexers and delegates. This article discusses these two powerful features of the C# programming language and how we can work with them.
When you call a method, constructor, indexer, or delegate, you must pass arguments for the required parameters but you are free to omit arguments for the parameters that have been defined as optional parameters.
Remembering the data types of the parameters as well as their position is cumbersome. The solution to this is to take advantage of named arguments and pass values to the method as shown in the code snippet given below.
Optional parameters in the C# programming language allow you to specify arguments in a method signature that the caller of the method is free to omit. In other words, while you must specify values for required parameters, you might choose not to specify values for optional parameters. In some cases, an optional parameter might have a default value associated with it as well.
The default value of an optional parameter may have any of three kinds of values: a constant expression, an expression that is of the form of a value type, or an expression that is of the form of default(v) where v is a value type.
Because two of the parameters in the Add method are optional, you can pass a single integer value to the method when calling it. Take care to follow the proper order of defining parameters in a method. The required parameters should come first, followed by optional parameters if any exist.
Named and optional parameters were introduced to the C# programming language in order to improve interoperability with COM APIs. Using named parameters can improve the readability of the source code. And you can take advantage of optional parameters as a replacement for using overloaded methods when the method definition is identical.
As the name suggests optional parameters are not compulsory parameters, they are optional. It helps to exclude arguments for some parameters. Or we can say in optional parameters, it is not necessary to pass all the parameters in the method. This concept is introduced in C# 4.0.
Explanation: In the above example, the scholar method contains four parameters out of these four parameters two are regular parameters, i.e. fname and lname and two are optional parameters, i.e. age and branch. These optional parameters contain their default values. When you do not pass the value of these parameters, then the optional parameters use their default value. And when you pass the parameters for optional parameters, then they will take the passed value not their default value.
A default argument is evaluated each time the function is called with no argument for the corresponding parameter. Function parameters are not allowed in default arguments except if they are not evaluated. Note that parameters that appear earlier in the parameter list are in scope:
Even in this limited form, named parameters would still be immenselyuseful, but this is not what this post is about. What this post isabout is that we can already achieve something very close to namedparameters in C++20, by using a C99 feature called designatedinitializers.
This means that earlier parameters can be referred to in the initializers of later parameters. However, functions and variables declared in the function body cannot be referred to from default value parameter initializers; attempting to do so throws a run-time ReferenceError. This also includes var-declared variables in the function body.
38c6e68cf9