Add project files.

EnumerablePerformance.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.3.32811.315
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EnumerablePerformance", "EnumerablePerformance\EnumerablePerformance.csproj", "{37DC452D-B053-4540-8AD4-DA7CB6A7E90B}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{37DC452D-B053-4540-8AD4-DA7CB6A7E90B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{37DC452D-B053-4540-8AD4-DA7CB6A7E90B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{37DC452D-B053-4540-8AD4-DA7CB6A7E90B}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{37DC452D-B053-4540-8AD4-DA7CB6A7E90B}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {B3DD8F12-987C-48AE-8397-DB44558BF61B}
+	EndGlobalSection
+EndGlobal

EnumerablePerformance/EnumerablePerformance.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

EnumerablePerformance/Program.cs

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+/*
+ * This method of enumerables makes it so that GetCustomers() is run twice, 
+ * doing the same read line and return of the same data, for two different 
+ * proccesses. Since customers is not immediately used, the function isn't 
+ * happening yet. Count() causes the first run of GetCustomers() in order
+ * to get the customers to receive the count. GetCustomers() is then rerun
+ * during the Console.WriteLine() where it retrieves each customer.
+ */
+
+Console.WriteLine("_______________________________________");
+Console.WriteLine("STANDARD");
+Console.WriteLine();
+
+
+var customers = GetCustomers();                     
+
+
+var count = customers.Count();
+Console.WriteLine($"\tThere are {count} customers");
+
+foreach(var customer in customers)
+{
+    Console.WriteLine("\t" + customer);
+}
+Console.WriteLine();
+
+/*
+ * By retrieving a list of the items from the function, you mitigate the issue
+ * of returning to the function later, as the data is saved as a list to a variable.
+ */
+
+Console.WriteLine("_______________________________________");
+Console.WriteLine("ENHANCED-PERFORMANCE");
+Console.WriteLine();
+
+
+var customersList = GetCustomersList();
+
+var countList = customersList.Count();
+Console.WriteLine($"\tThere are {countList} customers");
+
+foreach (var customer in customersList)
+{
+    Console.WriteLine("\t" + customer);
+}
+Console.WriteLine();
+
+
+// Functions
+
+IEnumerable<Customer> GetCustomers()
+{
+    Console.WriteLine("Inside GetCustomers()");
+    var lines = File.ReadAllLines("../../../customers.csv"); //For some reason the program starts an extra 2 deep into bin/Debug
+
+    foreach(var line in lines)
+    {
+        var splitLine = line.Split(",");
+        yield return new Customer(splitLine[0], int.Parse(splitLine[1]));
+    }
+}
+
+IEnumerable<Customer> GetCustomersList()
+{
+    Console.WriteLine("Inside GetCustomersList()");
+    var list = new List<Customer>();
+    var lines = File.ReadAllLines("../../../customers.csv"); //For some reason the program starts an extra 2 deep into bin/Debug
+
+    foreach (var line in lines)
+    {
+        var splitLine = line.Split(",");
+        list.Add(new Customer(splitLine[0], int.Parse(splitLine[1])));
+    }
+    return list;
+}
+
+
+
+
+record Customer(string Fullname, int Age);

EnumerablePerformance/customers.csv

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+Kira Jiroux,25
+Jira Kiroux,24
+Jairik Roux,59