using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        ExpandoString.AddVariable("test", "TEST");

        var test = new ExpandoString("This is a $(test)");

        Console.WriteLine(test);

    }

}

​

// You can define other methods, fields, classes and namespaces here

public class ExpandoString

{

    private static Regex _VariableRegex = new Regex(@"(\$\(\w+\))", RegexOptions.Compiled);

    private static MatchEvaluator _Evaluator;

    private static Dictionary<string, string> _Variables = new Dictionary<string, string>();

​

    static ExpandoString()

    {

        _Evaluator = new MatchEvaluator(ReplaceVariable);

    }

​

    public static void AddVariable(string variable, string value)

    {

        _Variables.Add(variable, value);

    }

​

    public static void AddOrUpdateVariable(string variable, string value)

    {

        _Variables[variable] = value;

    }

​

    public static string GetVariableValue(string variable)

    {

        if (_Variables.ContainsKey(variable))

        {

            return _Variables[variable];

        }

        return null;

    }

​

    public static string Expand(string input)

    {

        return _VariableRegex.Replace(input, _Evaluator);

    }

​

    private static string ReplaceVariable(Match match)

    {

        string replacement;

        if (_Variables.TryGetValue(match.Value.Substring(2).TrimEnd(')'), out replacement))

        {

            return replacement;

        }

        return match.Value;

    }

​

    private string _expanded;

​

    public string Original { get; private set; }

    public string Expanded

    {

        get

        {

            if (_expanded == null)

            {

                _expanded = Expand(Original);

            }

            return _expanded;

        }

    }

​

    public ExpandoString(string original)

    {

        Original = original;

    }

​

    public static implicit operator string(ExpandoString value) => value?.Expanded;

    public static implicit operator ExpandoString(string value) => new ExpandoString(value);

​

    public override string ToString()

    {

        return Expanded;

    }

​

    public override int GetHashCode()

    {

        return Expanded.GetHashCode();

    }

​

    public override bool Equals(object obj)

    {

        return Expanded.Equals(obj);

    }

}