Daily Knowledge Drop
There are numerous ways of handling the multiple case switch statement/expression in C#, and these various methods have evolved over time as C# language features have been introduced and enhanced.
Today we'll look at a few of these ways, specifically around having multiple cases returning the same result.
Switch statement
With the traditional switch statement, each case needs to be specified explicitly (except for the default case). This can become very long and tedious if there are many different cases. Prior to C#7, this was the only option:
public string TraditionalSwitch(int temperature)
{
if (temperature < 0)
{
return "Unnaturally cold";
}
switch (temperature)
{
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
return "Cold";
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
case 20:
return "Moderate";
case 21:
case 22:
case 23:
case 24:
case 25:
case 26:
case 27:
case 28:
case 29:
case 30:
return "Hot";
case 31:
case 32:
case 33:
case 34:
case 35:
case 36:
case 37:
case 38:
case 39:
case 40:
return "Very Hot";
default:
return "Surface of the sun";
}
}
Switch with when
C#7 introduced the ability to use the when keyword, in conjunction with and (&&) and or (||) operators, which simplified and reduced the amount of code:
public string WhenExpressionSwitch(int temperature)
{
switch (temperature)
{
case var t when temperature < 0:
return "Unnaturally cold";
case var t when temperature > 0 && temperature < 11:
return "Cold";
case var t when temperature > 11 && temperature < 21:
return "Moderate";
case var t when temperature > 21 && temperature < 31:
return "Hot";
case var t when temperature > 31:
return "Very Hot";
default:
return "Surface of the sun";
}
}
Switch assignment
C#8 introduced the ability to assign the value returned from a switch, instead of just using it to control logic flow:
public string AssignmentSwitchExpression(int temperature)
{
var result = temperature switch
{
var t when temperature < 0 => "Unnaturally cold",
var t when temperature > 0 && temperature < 11 => "Cold",
var t when temperature > 11 && temperature < 21 => "Moderate",
var t when temperature > 21 && temperature < 31 => "Hot",
var t when temperature > 31 => "Very Hot",
_ => "Surface of the sun"
};
return $"It is {result}";
}
Switch expression
C#8 also introduced the ability to create a switch expression from a method, again to simplify and reduce code:
public string SwitchExpression(int temperature) => temperature switch
{
_ when temperature < 0 => "Unnaturally cold",
_ when temperature > 0 && temperature < 11 => "Cold",
_ when temperature > 11 && temperature < 21 => "Moderate",
_ when temperature > 21 && temperature < 31 => "Hot",
_ when temperature > 31 => "Very Hot",
_ => "Surface of the sun"
};
In this example, the discard character (_), is also used instead of an unused variable as in the previous example.
Multi value switch expression
With C#8, multiple values can also be used when checking the switch condition. In the below example, the two values are converted to a tuple and then the tuple is used in the switch expression:
public string SwitchExpression(int temperature, SkyOutlook sky)
=> (temperature, sky) switch
{
_ when temperature < 0 && sky == SkyOutlook.Sunny => "Cold but hot",
_ when temperature < 0 && sky == SkyOutlook.Rainy => "Actually snowing",
_ when temperature > 31 && sky == SkyOutlook.Sunny => "Get to air-con",
_ => "Unable to determine"
};
Switch on a class - part 1
Another C#8 enhancement, was the ability to use a class in the switch expression and switch on a class property(s).
Consider a Person class which contains a person's name and age:
public string ClassSwitchExpression(Person person) => person switch
{
{ Age: < 10 } => "Younger than 10",
{ Age: < 20 } => "Younger than 20",
{ Age: < 30 } => "Younger than 30",
{ Age: < 50 } => "Younger than 50",
_ => "Older than 50"
};
Switch on a class - part 2
When using a class to switch on, its also possible to use properties of a child class in the condition.
Consider the Person class has a Country property, which is the Country class. The Country class has a Hemisphere property indicating northern or southern hemisphere:
public string EnhancedClassSwitchExpressionCountry(Person person) => person switch
{
{ Age: < 10 } => "Younger than 10",
{ Age: >= 10 and < 20 } => "Between 10 and 20",
{ Age: >= 20 and < 30, Country: { Hemisphere: "North" } } =>
"Between 19 and 30, living in north hemisphere",
{ Age: >= 20 and < 30, Country: { Hemisphere: "South" } } =>
"Between 19 and 30, living in south hemisphere",
{ Age: >= 30 and < 50 } => "Between 29 and 40",
_ => "Older than 50"
};
Switch on a class - part 3
C#10 cleaned up the syntax, which allowed for easier access to the properties of the child class:
public string EnhancedClassSwitchExpressionCountry2(Person person) => person switch
{
{ Age: < 10 } => "Younger than 10",
{ Age: >= 10 and < 20 } => "Between 10 and 20",
{ Age: >= 20 and < 30, Country.Hemisphere: "North" } =>
"Between 19 and 30, living in north hemisphere",
{ Age: >= 20 and < 30, Country.Hemisphere: "South" } =>
"Between 19 and 30, living in south hemisphere",
{ Age: >= 30 and < 50 } => "Between 29 and 40",
_ => "Older than 50"
};
Notes
From a basic switch statement to a switch expression, with multiple conditional enhancement the switch functionality has evolved and continues to evolve to make it more feature rich and easier to use for developers.
References
What's new in C# 8.0
What's new in C# 9.0
C#10 Extended property patterns
Daily Drop 29: 11-03-2022
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.