functional-workshop

functional programming principles applied in C#

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Pure Functions

It is said that a function is pure when its output depends entirely on the input parameters. And cause no side effects. Therefore they improve,

• Testability
• Correctness
• Readability

With no side effects there are no surprises. our code does what it says, no more. and the cognitive load to understand the code is less

internal class TestPureFunctions
{
    private const string A = "a";
    private const string B = "b";
    private const string AB = "ab";
    private const string ABAB = "abab";

    internal static void Run()
    {
        var ab = Join(A, B);
        // We can expect the same result always
        // if we pass the same parameters
        AreEqual(ab, AB);
        AreEqual(Join(A, B), AB);

        var abab = Join(AB, AB);
        // This also has an impact
        // on Referential Transparency
        AreEqual(abab, ABAB);
        AreEqual(Join(AB, AB), ABAB);
    }

    // This is a Pure Function
    private static string Join(string lhs, string rhs)
        => $"{lhs}{rhs}";

    // This is also a Pure Function
    private static bool AreEqual(string lhs, string rhs)
        => lhs == rhs;
}