New C# 7 features in action: Pattern matching in C# 7 – switch statements with patterns
Switch statement with C# 7’s pattern matching enhancements
Switch on any type
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public static bool DoPayment(object creditCard, decimal amount) { switch (creditCard) // // Switch on any type, here creditCard is of type object { // Some code. } } |
Case clauses with patterns
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switch (creditCard) // Switch on any type, here creditCard is of type object { case AmericanExpress amex: // Case clauses with type pattern "AmericanExpress amex" { success = amex.ProcessAmexPayment(amount); break; } } |
Case clauses with additional conditions on them
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switch (creditCard) // Switch on any type, here creditCard is of type object { case ICard card when card.IsValidCard == false: // Case clauses with type pattern "ICard card" and additional conditions { success = false; break; } } |
Case clauses – order is important
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switch (creditCard) // Switch on any type, here creditCard is of type object { case Visa visa when visa.IsCreditCard == false: // Evaluate before "case Visa visaCreditCard" { success = visa.ProcessVisaPayment(amount); break; } case Visa visaCreditCard: { success = visaCreditCard.ProcessVisaCreditCardPayment(amount); break; } } |
Null clause – to handle null values
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switch (creditCard) // Switch on any type, here creditCard is of type object { case null: // Null clause - to handle null values { success = false; // Code to handle null values break; } } |
Default clause always evaluated last
Simple Credit Card Processor Class (used to explain C# 7’s switch statement enhancements)
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using System; namespace SampleApplication { public interface ICard { bool IsValidCard { get; set; } } public class AmericanExpress : ICard { public bool IsValidCard { get; set; } public bool ProcessAmexPayment(decimal amount) { throw new NotImplementedException(); } } public class Visa : ICard { public bool IsValidCard { get; set; } public bool IsCreditCard { get; set; } public bool ProcessVisaPayment(decimal amount) { throw new NotImplementedException(); } public bool ProcessVisaCreditCardPayment(decimal amount) { throw new NotImplementedException(); } } public class MasterCard : ICard { public bool IsValidCard { get; set; } public bool IsCreditCard { get; set; } public bool ProcessMasterCardPayment(decimal amount) { throw new NotImplementedException(); } public bool ProcessMasterCreditCardPayment(decimal amount) { throw new NotImplementedException(); } } } |
Sample code to use C# 7’s pattern matching to enhance the switch statements
Note the use of pattern matching (in switch statement)
- Switch with object type (
switch (creditCard)) - Case clauses with type patterns (
case AmericanExpress amex:) - Case clauses with additional conditions on them (
case ICard card when card.IsValidCard == false:) - Null clause – to handle null values (
case null:) - Case clauses – here order is important
- Default clause always evaluated last
in the below sample code:
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namespace SampleApplication.CSharp7 { public partial class CSharp7Sample { public static bool DoPayment(object creditCard, decimal amount) { if (amount == 0) { return false; } bool success = false; switch (creditCard) // Switch on any type, here creditCard is of type object { case ICard card when card.IsValidCard == false: // Case clauses with type pattern "ICard card" and additional conditions { success = false; break; } case AmericanExpress amex: // Case clauses with type pattern "AmericanExpress amex" { success = amex.ProcessAmexPayment(amount); break; } case Visa visa when visa.IsCreditCard == false: { success = visa.ProcessVisaPayment(amount); break; } case Visa visaCreditCard: { success = visaCreditCard.ProcessVisaCreditCardPayment(amount); break; } case MasterCard masterCard when masterCard.IsCreditCard == false: { success = masterCard.ProcessMasterCardPayment(amount); break; } case MasterCard masterCreditCard: { success = masterCreditCard.ProcessMasterCreditCardPayment(amount); break; } case null: // Null clause - to handle null values { success = false; // Code to handle null values break; } default: // Default clause always evaluated last { success = false; break; } } return success; } } } |
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