rspec/rules/S1479/csharp/rule.adoc

== Why is this an issue?

When https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/selection-statements#the-switch-statement[switch] statements have large sets of case clauses, it is usually an attempt to map two sets of data. A https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2[Dictionary] should be used instead to make the code more readable and maintainable.

=== Exceptions

This rule ignores `switch` statements over `Enum` arguments and empty, fall-through cases.

== How to fix it

Store all the cases apart from the `default` one in a dictionary and try to get the matching value by calling the https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.trygetvalue[TryGetValue] method.

=== Code examples

The example below are using the "Maximum number of case" property set to `4`.

==== Noncompliant code example

[source,csharp,diff-id=1,diff-type=noncompliant]
----
public class TooManyCase
{
    public int mapValues(char ch)
    {
        switch(ch) {  // Noncompliant: 5 cases, "default" excluded, more than maximum = 4
            case 'a':
                return 1;
            case 'b':
            case 'c':
                return 2;
            case 'd':
                return 3;
            case 'e':
                return 4;
            case 'f':
            case 'g':
            case 'h':
                return 5;
            default:
                return 6;
        }
    }
}
----

==== Compliant solution

[source,csharp,diff-id=1,diff-type=compliant]
----
using System.Collections.Generic;

public class TooManyCase
{
    Dictionary<char, int> matching = new Dictionary<char, int>()
    {
        { 'a', 1 }, 
        { 'b', 2 }, 
        { 'c', 2 }, 
        { 'd', 3 },
        { 'e', 4 }, 
        { 'f', 5 }, 
        { 'g', 5 }, 
        { 'h', 5 }
    };

    public int mapValues(char ch)
    {
        int value;
        if (this.matching.TryGetValue(ch, out value)) {
            return value;
        } else {
            return 6;
        }
    }
}
----

include::../resources-dotnet.adoc[]
* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/selection-statements#the-switch-statement[The `switch` statement]

include::../rspecator-dotnet.adoc[]