Optional method parameters

Daily Knowledge Drop

In additional to giving a parameter a default value, so that it can be omitted when calling a method, the Optional attribute can also be used allow for parameter omission.

Parameter default values

When defining a method, the parameters can be given a default value. This allows for the parameter to be omitted when calling the method:

// both required
MethodNoDefaults("John", 50);

// all parameters are required when calling this method
void MethodNoDefaults(string name, int age)
{
    Console.WriteLine($"Parameters: Name='{name}', Age='{age}'");
}

//----------------------------------------

// name required, age optional
MethodOneDefaultValue("John");

// only the name parameter is required, age can be omitted
// if omitted, the value of age will be -1
void MethodOneDefaultValue(string name, int age = -1)
{
    Console.WriteLine($"Parameters: Name='{name}', Age='{age}'");
}

//----------------------------------------

// all parameters are optional
MethodAllDefaultValues("John");
MethodAllDefaultValues(age:20);
MethodAllDefaultValues();

// both parameters are optional and can be omitted
void MethodAllDefaultValues(string name = "", int age = -1)
{
    Console.WriteLine($"Parameters: Name='{name}', Age='{age}'");
}

The output for the above method calls:

Parameters: Name='John', Age='50'
Parameters: Name='John', Age='-1'
Parameters: Name='John', Age='-1'
Parameters: Name='', Age='20'
Parameters: Name='', Age='-1'

One limitation of using the default value approach, is that optional parameters must appear after all required parameters. This might force the order of the parameters into an unwanted sequence.

Optional attribute

Instead of using default values, the Optional attribute can also be used to mark a parameter as optional:

MethodOneOptional("John", 20);
MethodOneOptional(age: 40);

// first parameter is optional
void MethodOneOptional([Optional]string name, int age)
{
    Console.WriteLine($"Parameters: Name='{name}', Age='{age}'");
}

//----------------------------------------

MethodAllOptional();

// all parameters are optional
void MethodAllOptional([Optional] string name, [Optional] int age)
{
    Console.WriteLine($"Parameters: Name='{name}', Age='{age}'");
}

The output being:

Parameters: Name='John', Age='20'
Parameters: Name='', Age='40'
Parameters: Name='', Age='0'

One advantage of using the Optional attribute, is that optional parameters can appear anywhere in the sequence of attributes, even before required parameters.

The disadvantage is that a default value cannot be specified for optional parameters and the type default value will be used.

Notes

The Optional attribute is another great option to know about, to be leveraged in the appropriate use case.

Daily Drop 22: 02-03-2022

At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.

The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.