{"id":599,"date":"2022-04-29T13:31:00","date_gmt":"2022-04-29T13:31:00","guid":{"rendered":"https:\/\/andrejacobs.org\/?p=599"},"modified":"2022-05-27T15:53:54","modified_gmt":"2022-05-27T15:53:54","slug":"learning-go-day-9","status":"publish","type":"post","link":"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/","title":{"rendered":"Learning Go &#8211; Day 9"},"content":{"rendered":"\n<p class=\"has-small-font-size\">Featured image by&nbsp;<a href=\"https:\/\/github.com\/egonelbre\/gophers\" target=\"_blank\" rel=\"noreferrer noopener\">Egon Elbre<\/a><\/p>\n\n\n\n<div class=\"wp-block-jetpack-markdown\"><ul>\n<li>\n<p>In all my life of using mkdir -p, I never knew you can create multiple subdirectories the easy way. <strong>UPDATE:<\/strong> This is actually the shell doing some path expansion and thus can work anywhere.<\/p>\n<pre><code class=\"language-go\">$ mkdir -p ~\/temp\/some\/path\/{dir1,dir2,dir3\/even\/more}\n\n$ tree ~\/temp\/some\n\/Users\/andre\/temp\/some\n\u2514\u2500\u2500 path\n    \u251c\u2500\u2500 dir1\n    \u251c\u2500\u2500 dir2\n    \u2514\u2500\u2500 dir3\n        \u2514\u2500\u2500 even\n            \u2514\u2500\u2500 more\n<\/code><\/pre>\n<\/li>\n<li>\n<p>Use <code>os.CreateTemp()<\/code> to create a temporary file on the system. You can specify a directory if needed and also a file name pattern the will be randomised. E.g \u201cconfig_*.json\u201d<\/p>\n<\/li>\n<li>\n<p>You can also use <code>os.os.MkdirTemp()<\/code> to create a temporary directory.<\/p>\n<\/li>\n<li>\n<p>Go comes with template rendering for HTML and Text.<\/p>\n<\/li>\n<li>\n<p>Learned a little bit about Colly &#8211; the web scraping package for Go.<\/p>\n<\/li>\n<\/ul>\n<h3>Working with file systems<\/h3>\n<ul>\n<li>Use the package <code>path\/filepath<\/code> to work agnostically with the system\u2019s file path. E.g. this takes into account that Windows uses <code>\\<\/code> versus Unix based os uses `<\/li>\n<li>You can use <code>filepath.Walk<\/code> to recursively walk a directory and it will call the function you specify on each found file or directory. There is a note that WalkDir performs better.\nSee the documentation for <a href=\"https:\/\/pkg.go.dev\/path\/filepath?utm_source=gopls#WalkFunc\">WalkFunc<\/a>.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">filepath.Walk(&quot;.\/somewhere\/here&quot;,\n\t\tfunc(path string, info fs.FileInfo, err error) error {\n\t\t\tif err != nil {\n\t\t\t\treturn err\n\t\t\t}\n\n\t\t\t\/\/ See the WalkFunc documentation for what this function can do to control\n\t\t\t\/\/ how the Walk behaves\n\t\t}\n}\n<\/code><\/pre>\n<ul>\n<li>fs.FileInfo is declared as:<\/li>\n<\/ul>\n<pre><code class=\"language-go\">type FileInfo interface {\n\tName() string       \/\/ base name of the file\n\tSize() int64        \/\/ length in bytes for regular files; system-dependent for others\n\tMode() FileMode     \/\/ file mode bits\n\tModTime() time.Time \/\/ modification time\n\tIsDir() bool        \/\/ abbreviation for Mode().IsDir()\n\tSys() any           \/\/ underlying data source (can return nil)\n}\n<\/code><\/pre>\n<ul>\n<li>To get just the file extension. Use <code>filepath.Ext()<\/code><\/li>\n<\/ul>\n<pre><code class=\"language-go\">import &quot;path\/filepath&quot;\n\nfmt.Println(filepath.Ext(&quot;\/dir\/filename.txt&quot;)) \/\/ .txt\nfmt.Printf(&quot;%q&quot;, filepath.Ext(&quot;\/dir\/filename&quot;)) \/\/ &quot;&quot; &lt;- note it is empty string\n\n<\/code><\/pre>\n<ul>\n<li>Recall from earlier you can use <code>os.Remove()<\/code> to delete a single file. You can also use <code>os.RemoveAll()<\/code> to recursively delete a directory.<\/li>\n<\/ul>\n<h3>Unit-testing<\/h3>\n<p>Gophers (Go programmers) use this concept called \u201cTable-Driven testing\u201d by which you build up a table of inputs and expected outputs and then in your unit-test you iterate over the table and check that feeding inputs produce the expected outputs.<\/p>\n<p>I like this and can already see many places where I can apply the same idea to my Swift and other languages.<\/p>\n<p>See <a href=\"https:\/\/dave.cheney.net\/2019\/05\/07\/prefer-table-driven-tests\">Dave Cheney\u2019s article<\/a> on this.<\/p>\n<p>Note: You can also use <code>t.Run(nameOfTest, func (t *testing.T) { ... } )<\/code> to run sub tests inside of a unit-test. Couple this with the <code>for _, testCase := range testCases<\/code> and you have super powers.<\/p>\n<ul>\n<li>You can define Helper functions for your unit-tests. They are usefull for reusing the same code in multiple unit-tests but also if the helper raises errors like <code>t.Fatal()<\/code> then the line number etc. is reported as the unit-test that called the helper and not the helper function it self.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">func iamAHelper(t *testing.T, someOtherArgs string) {\n\tt.Helper() \/\/ mark this as a helper\n\t\/\/ so that calls like this, will output line etc. where this helper was called\n\tt.Fatal(someError)\n}\n<\/code><\/pre>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Featured image by&nbsp;Egon Elbre [&#8230;]<\/p>\n<p><a class=\"understrap-read-more-link\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/\">Read more &rarr;<\/a><\/p>\n","protected":false},"author":2,"featured_media":583,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[52],"tags":[53],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v19.13 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Learning Go - Day 9 - Andr\u00e9 Jacobs<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Learning Go - Day 9 - Andr\u00e9 Jacobs\" \/>\n<meta property=\"og:description\" content=\"Featured image by&nbsp;Egon Elbre [...]Read more &rarr;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/\" \/>\n<meta property=\"og:site_name\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta property=\"article:published_time\" content=\"2022-04-29T13:31:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2022-05-27T15:53:54+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/05\/messenger-reading.png\" \/>\n\t<meta property=\"og:image:width\" content=\"552\" \/>\n\t<meta property=\"og:image:height\" content=\"660\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:site\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Andr\u00e9 Jacobs\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-9\/\"},\"author\":{\"name\":\"Andr\u00e9 Jacobs\",\"@id\":\"https:\/\/andrejacobs.org\/#\/schema\/person\/3d38360883015e883c80c2fb875c5a68\"},\"headline\":\"Learning Go &#8211; 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