{"id":557,"date":"2022-04-17T10:22:00","date_gmt":"2022-04-17T10:22:00","guid":{"rendered":"https:\/\/andrejacobs.org\/?p=557"},"modified":"2022-04-22T10:25:46","modified_gmt":"2022-04-22T10:25:46","slug":"learning-go-day-2","status":"publish","type":"post","link":"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-2\/","title":{"rendered":"Learning Go &#8211; Day 2"},"content":{"rendered":"\n<p class=\"has-small-font-size\">Featured image by\u00a0<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\"><p>Happy Easter!<\/p>\n<ul>\n<li>Continuing to work through <a href=\"https:\/\/golangbot.com\/learn-golang-series\/\">https:\/\/golangbot.com\/learn-golang-series\/<\/a>\n<ul>\n<li>Tutorials 13 to 15.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Maps<\/h3>\n<ul>\n<li>Used as a mapping between key-value pairs. Aka Dictionary in other languages.<\/li>\n<li>Creating a map<\/li>\n<\/ul>\n<pre><code class=\"language-go\">\/\/ make(map[keyType]valueType)\n\nnameToAge := make(map[string]int)\n\n\/\/ short hand declaration\nfileSizes := map[string]int{\n\t&quot;file1.txt&quot;: 104,\n\t&quot;file2.txt&quot;: 4224, \/\/&lt;-- notice the trailing comma!\n}\n<\/code><\/pre>\n<ul>\n<li>Adding items to the map or updating existing values<\/li>\n<\/ul>\n<pre><code class=\"language-go\">nameToAge[&quot;jannie&quot;] = 23\nnameToAge[&quot;koos&quot;] = 34\nfmt.Println(nameToAge) \/\/ map[jannie:23 koos:34]\n\nnameToAge[&quot;jannie&quot;] = 42\nfmt.Println(nameToAge) \/\/ map[jannie:42 koos:34]\n<\/code><\/pre>\n<ul>\n<li>Any comparable type is allowed to be used as a key type. Including your own \u201cstruct\u201d types.<\/li>\n<li>The zero value of a map is <code>nil<\/code> and maps have to be initialized first.<\/li>\n<li>Getting items from a map.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">ageForKoos := nameToAge[&quot;koos&quot;]\n\n\/\/ What about when the key does not exist?\n\/\/ It returns the zero value of the type\nfmt.Println(fileSizes[&quot;unknown&quot;]) \/\/ 0\n<\/code><\/pre>\n<ul>\n<li>Checking if an item exists in the map.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">value, ok := nameToAge[&quot;unknown&quot;]\nif ok {\n... \/\/ key &quot;unknown&quot; existed and we received a value in value\n}\n\n\/\/ or to just check if key is present\n_, exists := someMap[someKey]\nif exists { ...\n<\/code><\/pre>\n<ul>\n<li>Iterating over the key-value pairs<\/li>\n<\/ul>\n<pre><code class=\"language-go\">for key, value := range nameToAge {\n...\n}\n<\/code><\/pre>\n<ul>\n<li>Map is unordered.<\/li>\n<li>Use <code>delete(map, key)<\/code> function to delete an item from a map.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">delete(nameToAge, &quot;koos&quot;)\n\n\/\/ No runtime error is raised if you delete a non existent key\n\/\/ Also delete doesn't return a value to check if the key was deleted\ndelete(nameToAge, &quot;no-error&quot;)\n<\/code><\/pre>\n<ul>\n<li>Use <code>len(map)<\/code> function to get the key count.<\/li>\n<li><strong>NOTE:<\/strong> Maps are reference types (unlike Swift). Meaning that if you assign a map to multiple variables (or pass to functions) then changes made to one will reflect to all of them (since they are references to the actual data).<\/li>\n<li>Maps can not be compared using <code>==<\/code> operator. The <code>==<\/code> operator can only be used to check if the map is <code>nil<\/code><\/li>\n<\/ul>\n<h3>Strings<\/h3>\n<ul>\n<li>Strings are implemented as a slice of bytes in Go.<\/li>\n<li><code>string<\/code> is the type.<\/li>\n<li>Strings are unicode compliant and encoded as UTF-8.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">name := &quot;Andre Jacobs&quot;\nfmt.Printf(&quot;my name is %s\\n&quot;, name)\n<\/code><\/pre>\n<ul>\n<li>Use <code>len()<\/code> to get the number of bytes in the string.<\/li>\n<li><strong>NOTE:<\/strong> Iterating over the bytes of a string is not the same as iterating over \u201ccharacters\u201d or unicode code points (as what Swift does).<\/li>\n<li>To iterate over the unicode code points, you will use the <code>rune<\/code> type (alias to <code>int32<\/code>).<\/li>\n<\/ul>\n<pre><code class=\"language-go\">func printCharacters(s string) {  \n    runes := []rune(s)\n    for i := 0; i &lt; len(runes); i++ {\n        fmt.Printf(&quot;%c &quot;, runes[i])\n    }\n}\n\n\/\/ A much better way is to use range\nfor index, rune := range s {\n...\n}\n<\/code><\/pre>\n<ul>\n<li>Creating a string from a slice of bytes.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">byteSlice := []byte{0x43, 0x61, 0x66, 0xC3, 0xA9}\nstr := string(byteSlice)\n<\/code><\/pre>\n<ul>\n<li>Creating a string from a slice of runes.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">runeSlice := []rune{0x0053, 0x0065, 0x00f1, 0x006f, 0x0072}\nstr := string(runeSlice)\n<\/code><\/pre>\n<ul>\n<li>Use <code>RuneCountInString()<\/code> function from package \u201cunicode\/utf8\u201d to get the number of unicode \u201ccharacters\u201d in a string.<\/li>\n<li>You can use <code>==<\/code> to check for equality. (May assumption is Go just compares the bytes and no the grapheme clusters like Swift does).<\/li>\n<li>You can concatenate strings using <code>+<\/code> operator. You can also use fmt.Sprintf function.<\/li>\n<li>String are immutable.<\/li>\n<\/ul>\n<h3>Pointers<\/h3>\n<ul>\n<li>Quick recap: A pointer is a variable that stores an address to some location in memory (that can then be mapped to a type).<\/li>\n<li>Declared using <code>*T<\/code>.<\/li>\n<li>Use <code>&amp;<\/code> to get the address of a variable.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">b := 255\nvar a *int = &amp;b \/\/ create a pointer to b\nfmt.Printf(&quot;Type of a is %T\\n&quot;, a) \/\/ Type of a is *int\nfmt.Println(&quot;address of b is&quot;, a) \/\/ address of b is 0xc000018030\n<\/code><\/pre>\n<ul>\n<li>Zero value of a pointer is <code>nil<\/code>.<\/li>\n<li>Allocate a new instance and assign to a pointer using <code>new<\/code> function.<\/li>\n<li>Dereference using <code>*<\/code> just like C.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">p := new(int)\nfmt.Printf(&quot;%T\\n&quot;, p) \/\/ *int\nfmt.Println(p) \/\/ 0xc000018038\nfmt.Println(*p) \/\/ 0\n\n*p = 42\nfmt.Println(*p) \/\/ 42\n<\/code><\/pre>\n<ul>\n<li>Pointers can be passed as function arguments.<\/li>\n<li>Pointers can also be returned as the result type for a function.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">\/\/ What do you think this code will do?\nfunc spideySense() *int {\n    i := 5\n    return &amp;i\n}\n\n\/\/ Go is smart enough to save you from the C pitfalls here and\n\/\/ allocates i on the heap!\n<\/code><\/pre>\n<ul>\n<li>It is more Go idiomatic to pass slices of arrays to functions (instead of passing a pointer to an array).<\/li>\n<li>Go does not support pointer arithmetic like C does.<\/li>\n<\/ul>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Featured image by\u00a0Egon Elbre [&#8230;]<\/p>\n<p><a class=\"understrap-read-more-link\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-2\/\">Read more &rarr;<\/a><\/p>\n","protected":false},"author":2,"featured_media":551,"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 2 - 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-2\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Learning Go - Day 2 - Andr\u00e9 Jacobs\" \/>\n<meta property=\"og:description\" content=\"Featured image by\u00a0Egon Elbre [...]Read more &rarr;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-2\/\" \/>\n<meta property=\"og:site_name\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta property=\"article:published_time\" content=\"2022-04-17T10:22:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2022-04-22T10:25:46+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/04\/pirate-lifting-goods.png\" \/>\n\t<meta property=\"og:image:width\" content=\"514\" \/>\n\t<meta property=\"og:image:height\" content=\"669\" \/>\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=\"4 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-2\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-2\/\"},\"author\":{\"name\":\"Andr\u00e9 Jacobs\",\"@id\":\"https:\/\/andrejacobs.org\/#\/schema\/person\/3d38360883015e883c80c2fb875c5a68\"},\"headline\":\"Learning Go &#8211; 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