{"id":459,"date":"2009-09-22T00:36:41","date_gmt":"2009-09-21T23:36:41","guid":{"rendered":"http:\/\/blog.eweibel.net\/?p=459"},"modified":"2009-09-22T00:44:32","modified_gmt":"2009-09-21T23:44:32","slug":"fail-fast-principle","status":"publish","type":"post","link":"https:\/\/blog.eweibel.net\/?p=459","title":{"rendered":"Fail Fast principle"},"content":{"rendered":"

Recently I received a NullReference-Exception when I called another method from a foreign component. Fortunately I had the source code of this component and I found the following code:
\n[code language=”csharp”]
\npublic class AgeValidator
\n{
\n\tpublic Dictionary Config { get; set; }<\/p>\n

\tpublic bool Validate(int nAge)
\n\t{
\n\t\tint nMinAge = FindValue(“MinAge”);<\/p>\n

\t\treturn nAge > nMinAge;
\n\t}<\/p>\n

\tprivate int FindValue(string strParameter)
\n\t{
\n\t\tint nValue = -1;<\/p>\n

\t\tif(this.Config.ContainsKey(strParameter)) nValue = this.Config[strParameter];<\/p>\n

\t\treturn nValue;
\n\t}
\n}
\n[\/code]<\/p>\n

There are several problems with this code. First, there are no preconditions which checks if the object is in a valid state or the parameters are valid. This cause to behaviour which isn’t intended. The problem with a not available configuration could already detect in the Validate method. The Find method could check if the parameter is valid, if not it doesn’t make any sense to continue. The FindValue method doesn’t follow the Fail Fast principle<\/a>. Jim Shore wrote an excellent article<\/a> about the Fail Fast principle. After a refactoring the code looks like that:
\n[code language=”csharp”]
\npublic class AgeValidator
\n{
\n\tpublic Dictionary Config { get; set; }<\/p>\n

\tpublic bool Validate(int nAge)
\n\t{
\n\t\tif(this.Config == null || this.Config.Keys.Count == 0) throw new InvalidOperationException(“No valid configuration available.”);<\/p>\n

\t\tint nMinAge = FindValue(“MinAge”);<\/p>\n

\t\treturn nAge > nMinAge;
\n\t}<\/p>\n

\tprivate int FindValue(string strParameter)
\n\t{
\n\t\tif(string.IsNullOrEmpty(strParameter)) throw new ArgumentNullException(“strParameter”);
\n\t\tif(!this.Config.ContainsKey(strParameter)) throw new ArgumentException(string.Format(“No configuration for the key ‘{0}’ found.”, strParameter));<\/p>\n

\t\treturn this.Config[strParameter];
\n\t}
\n}
\n[\/code]<\/p>\n

What I advise junior software developers is to follow the Fail Fast principle, disciplined use of preconditions and if it adequate the use of postconditions. But all these advices don’t replacing unit testing.<\/p>\n","protected":false},"excerpt":{"rendered":"

Recently I received a NullReference-Exception when I called another method from a foreign component. Fortunately I had the source code of this component and I found the following code: [code language=”csharp”] public class AgeValidator { public Dictionary Config { get; set; } public bool Validate(int nAge) { int nMinAge = FindValue(“MinAge”); return nAge > nMinAge; } private int FindValue(string strParameter) { int nValue = -1; if(this.Config.ContainsKey(strParameter)) nValue = this.Config[strParameter]; return nValue; } } [\/code] There are several problems with this…<\/p>\n

Read More Read More<\/span><\/a><\/p>\n","protected":false},"author":2,"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,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5,14],"tags":[],"class_list":["post-459","post","type-post","status-publish","format-standard","hentry","category-good-practices","category-software-engineering"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/plOV9-7p","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":942,"url":"https:\/\/blog.eweibel.net\/?p=942","url_meta":{"origin":459,"position":0},"title":"Enums and inheritance in .Net","author":"Patrick","date":"9. Feb 2011","format":false,"excerpt":"In one of my current projects I had the following code (I simplified the code a bit): public string ConnectionString { get { switch(this.Importer) { case Importer.SqlServer: return \"Server=localhost;Database=Northwind\"; case Importer.SqlServerOleDb: return\"Provider=SQLOLEDB;Data Source=localhost;Initial Catalog=Northwind\"; default: throw new NotSupportedException( string.Format(\"Importer {0} is not supported yet.\", this.Importer)); } } } After running\u2026","rel":"","context":"In ".NET"","block_context":{"text":".NET","link":"https:\/\/blog.eweibel.net\/?cat=13"},"img":{"alt_text":"CodeCoverage","src":"https:\/\/i0.wp.com\/blog.eweibel.net\/wp-content\/uploads\/CodeCoverage_thumb.png?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/blog.eweibel.net\/wp-content\/uploads\/CodeCoverage_thumb.png?resize=350%2C200 1x, https:\/\/i0.wp.com\/blog.eweibel.net\/wp-content\/uploads\/CodeCoverage_thumb.png?resize=525%2C300 1.5x"},"classes":[]},{"id":1182,"url":"https:\/\/blog.eweibel.net\/?p=1182","url_meta":{"origin":459,"position":1},"title":"Anti-Pattern ‘Validation by Execute ‘n’ Rollback’","author":"Patrick","date":"21. Feb 2012","format":false,"excerpt":"Recently in some reviews I saw an anti-pattern. First you have to know, in the code, there was a validation of the data before it was stored in the database. So far so good. But when I looked at the validation code, I saw the following: public void Validate() {\u2026","rel":"","context":"In "Anti patterns"","block_context":{"text":"Anti patterns","link":"https:\/\/blog.eweibel.net\/?cat=8"},"img":{"alt_text":"Fotolia_20233238_S","src":"https:\/\/i0.wp.com\/blog.eweibel.net\/wp-content\/uploads\/Fotolia_20233238_S_thumb1.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":17,"url":"https:\/\/blog.eweibel.net\/?p=17","url_meta":{"origin":459,"position":2},"title":"Get the size of your tables","author":"Patrick","date":"17. Jan 2008","format":false,"excerpt":"Recently my boss asked me, why the databases (Microsoft SQL Server 2005) of our customers are so big. With the following SQL-Statements I could give more or less an answer to my boss. CREATE TABLE PW_SPACE( name varchar(255), rows int, reserved varchar(255), data varchar(255), index_size varchar(255), unused varchar(255) ) GO\u2026","rel":"","context":"In "First experiencies"","block_context":{"text":"First experiencies","link":"https:\/\/blog.eweibel.net\/?cat=7"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":376,"url":"https:\/\/blog.eweibel.net\/?p=376","url_meta":{"origin":459,"position":3},"title":"Mocking frameworks in .Net","author":"Patrick","date":"30. Mar 2010","format":false,"excerpt":"A few month ago I played with some mocking frameworks in .Net. There are already some comparisons available (here, here or here). In this blog post I want to show which frameworks are available and which one fits best for agile development. You could download the source code from github.com.\u2026","rel":"","context":"In ".NET"","block_context":{"text":".NET","link":"https:\/\/blog.eweibel.net\/?cat=13"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":622,"url":"https:\/\/blog.eweibel.net\/?p=622","url_meta":{"origin":459,"position":4},"title":"Branching practices","author":"Patrick","date":"6. Apr 2010","format":false,"excerpt":"In an environment where several developers work at the same code base or several features have to be implemented, then branching will be a topic. I was asked to create a branching guide for my current employer which use TFS as source code repository. 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I wasn't really surprised that there wasn't one unique opinion.One opinion was that 100% is a good\u2026","rel":"","context":"In "Software architecture"","block_context":{"text":"Software architecture","link":"https:\/\/blog.eweibel.net\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/posts\/459","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=459"}],"version-history":[{"count":12,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/posts\/459\/revisions"}],"predecessor-version":[{"id":471,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=\/wp\/v2\/posts\/459\/revisions\/471"}],"wp:attachment":[{"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=459"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=459"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.eweibel.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=459"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}