using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var str = "Her name is @name and she's @age years old";

        var parameters = new Dictionary<string, object>();

        parameters.Add("@name", "Lisa");

        parameters.Add("@age", 10);

        str = parameters.Aggregate(str, (current, parameter)=> current.Replace(parameter.Key, parameter.Value.ToString()));

        str = str.Format(parameters);

        Console.WriteLine(str);

        var str2 = new StringFormatter("Her name is @name and she's @age years old");

        str2.Add("@name", "Lisa");

        str2.Add("@age", 10);

        Console.WriteLine(str2);

    }

}

​

public class StringFormatter{

    public string Str {get;set;}

    public Dictionary<string, object> Parameters {get;set;}

    public StringFormatter(string p_str){

        Str = p_str;

        Parameters = new Dictionary<string, object>();

    }

    public void Add(string key, object val){

        Parameters.Add(key, val);

    }

    public override string ToString(){

        return Parameters.Aggregate(Str, (current, parameter)=> current.Replace(parameter.Key, parameter.Value.ToString()));

    }

}

​

public static class Helpers{

    public static string Format(this string str, IDictionary<string, object> parameters){

        return parameters.Aggregate(str, (current, parameter)=> current.Replace(parameter.Key, parameter.Value.ToString()));

    }

}