{"id":510,"date":"2019-01-08T18:05:43","date_gmt":"2019-01-08T22:05:43","guid":{"rendered":"http:\/\/www.tayloraliss.com\/blog\/?p=510"},"modified":"2019-01-08T18:07:24","modified_gmt":"2019-01-08T22:07:24","slug":"welcoming-the-delegates","status":"publish","type":"post","link":"https:\/\/www.tayloraliss.com\/blog\/?p=510","title":{"rendered":"Welcoming the delegates"},"content":{"rendered":"\n

I have started working through The Art of Unit Testing<\/a> by Roy Osherove and came upon this test that took me a while to understand:<\/p>\n\n\n\n

[Test] \npublic void IsValidFileName_EmptyFileName_Throws()\n{\n    var ex = Assert.Catch<Exception>(() => la.IsValidLogFileName(\"\"));                 \n    StringAssert.Contains(\"filename has to be provided\", ex.Message);\n}<\/pre>\n\n\n\n
I was really confused about what was happening on line 4. Looking at the NUnit documentation<\/a>, I saw that this is format for the Assert.Catch<\/code> method:<\/p>\n\n\n\n
T Assert.Catch<T>(TestDelegate code);<\/pre>\n\n\n\n
The method is going to return an exception, but it needs to be passed a TestDelegate<\/code> first. We can see the syntax for a TestDelegate<\/code> here<\/a>:<\/p>\n\n\n\n
public delegate Void TestDelegate ()<\/pre>\n\n\n\n
This seems strange because according to the code, Assert.Catch<\/code> is being passed a lambda expression: <\/p>\n\n\n\n
() => la.IsValidLogFileName(\"\")<\/pre>\n\n\n\n
Well it turns out<\/a> that Lambda expressions are a simpler syntax for anonymous delegates and can be used everywhere an anonymous delegate can be used. The Microsoft docs<\/a> even say as much:<\/p>\n\n\n\n
a lambda expression is just another way of specifying a delegate<\/p><\/blockquote>\n\n\n\n
The question is then, “what is a delegate?”  From my research<\/a>, a delegate is used in C# when you want to pass a function itself as a parameter. You often see people refer to a delegate as “a pointer to a function.” The syntax for creating a delegate is as follows:<\/p>\n\n\n\n
<access modifier> delegate <return type> <delegate_name>(<parameters>)<\/pre>\n\n\n\n
And here is some example code using a delegate:<\/p>\n\n\n\n
<\/p>\n\n\n\n
 class Program\n {\n     public delegate void Print(int value);\n\n     static void Main(string[] args)\n     {\n         Print printDel = PrintNumber;\n\n         \/\/ or you can do this:\n        \/\/ Print printDel = new Print(PrintNumber);\n\n        printDel(100000);\n        printDel(200);\n\n        printDel = PrintMoney;\n\n        printDel(10000);\n        printDel(200);\n    }\n\n    public static void PrintNumber(int num)\n    {\n        Console.WriteLine(\"Number: {0,-12:N0}\",num);\n    }\n\n    public static void PrintMoney(int money)\n    {\n        Console.WriteLine(\"Money: {0:C}\", money);\n    }\n}<\/pre>\n\n\n\n
And here is the output:<\/p>\n\n\n\n
Number: 10,000 \nNumber: 200 \nMoney: $ 10,000.00 \nMoney: $ 200.00 <\/pre>\n\n\n\n
Let’s understand what’s happening here.<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
  1. We are declaring a delegate called Print<\/code> that takes an integer as an argument. We create a new instance of this delegate can call it printDel<\/code>.<\/li>
  2. We point printDel<\/code> at the PrintNumber<\/code> function.<\/li>
  3. We call our delegate twice, passing it in two different values. It formats the numbers appropriately with commas as specified in the PrintNumber<\/code> method.<\/li>
  4. We then point printDel<\/code> at the PrintMoney<\/code> function.<\/li>
  5. We call our delegate two more times and this time<\/em> it formats the numbers for currency as described in the PrintMoney<\/code> function.<\/li><\/ol>\n\n\n\n
    So, in summary, if we use a delegate, we’re passing a pointer to chunk of code, whereas if we use a lambda, we’re passing the code directly (and anonymously). Lambdas are more convenient in this case because we don’t have to declare them or even give them a name.<\/p>\n","protected":false},"excerpt":{"rendered":"
    I have started working through The Art of Unit Testing by Roy Osherove and came upon this test that took me a while to understand: I was really confused about what was happening on line 4. Looking at the NUnit documentation, I saw that this is format for the Assert.Catch method: The method is going […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-510","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/510","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=510"}],"version-history":[{"count":10,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/510\/revisions"}],"predecessor-version":[{"id":549,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/510\/revisions\/549"}],"wp:attachment":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=510"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=510"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=510"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}