{"id":12045,"date":"2022-09-29T10:48:22","date_gmt":"2022-09-29T05:18:22","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-json-unmarshal-interface-pointer-with-later-type-assertion\/"},"modified":"2022-09-29T10:48:22","modified_gmt":"2022-09-29T05:18:22","slug":"solved-json-unmarshal-interface-pointer-with-later-type-assertion","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-json-unmarshal-interface-pointer-with-later-type-assertion\/","title":{"rendered":"[Solved] json.Unmarshal interface pointer with later type assertion"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-56676821\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"56676821\" data-parentid=\"56673166\" data-score=\"1\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>An empty interface isn&#8217;t an actual type, it&#8217;s basically something that matches anything.  As stated in the comments, a pointer to an empty interface doesn&#8217;t really make sense as a pointer already matches an empty interface since everything matches an empty interface.  To make your code work, you should remove the interface wrapper around your struct, since that&#8217;s just messing up the json type checking, and the whole point of an empty interface is that you can pass <em>anything<\/em> to it.<\/p>\n<pre><code>package main\n\nimport (\n    \"bytes\"\n    \"encoding\/json\"\n    \"fmt\"\n    \"io\"\n    \"io\/ioutil\"\n    \"log\"\n)\n\ntype myStruct struct {\n    A string `json:\"a\"`\n    B string `json:\"b\"`\n}\n\nfunc main() {\n    jsonBlob := []byte(`{\"a\":\"test\",\"b\":\"test2\"}`)\n\n    var foo = &amp;myStruct{} \/\/ This need to be a pointer so its attributes can be assigned\n    closer := ioutil.NopCloser(bytes.NewReader(jsonBlob))\n\n    err := unmarshalCloser(closer, foo)\n    if err != nil {\n        log.Fatal(err)\n    }\n    fmt.Println(fmt.Sprintf(\"%v\", foo))\n\n    \/\/ That\u00b4s what i want:\n    fmt.Println(foo.A)\n}\n\n\/\/ You don't need to declare either of these arguments as pointers since they're both interfaces\nfunc unmarshalCloser(closer io.ReadCloser, v interface{}) error {\n    defer closer.Close()\n    \/\/ v NEEDS to be a pointer or the json stuff will barf\n\n    \/\/ Simplified with the decoder\n    return json.NewDecoder(closer).Decode(v)\n}\n<\/code><\/pre>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">1<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved json.Unmarshal interface pointer with later type assertion <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] An empty interface isn&#8217;t an actual type, it&#8217;s basically something that matches anything. As stated in the comments, a pointer to an empty interface doesn&#8217;t really make sense as a pointer already matches an empty interface since everything matches an empty interface. To make your code work, you should remove the interface wrapper around &#8230; <a title=\"[Solved] json.Unmarshal interface pointer with later type assertion\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-json-unmarshal-interface-pointer-with-later-type-assertion\/\" aria-label=\"More on [Solved] json.Unmarshal interface pointer with later type assertion\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[596,356,2742],"class_list":["post-12045","post","type-post","status-publish","format-standard","hentry","category-solved","tag-go","tag-json","tag-unmarshalling"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] json.Unmarshal interface pointer with later type assertion - JassWeb<\/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:\/\/jassweb.com\/solved\/solved-json-unmarshal-interface-pointer-with-later-type-assertion\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] json.Unmarshal interface pointer with later type assertion - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] An empty interface isn&#8217;t an actual type, it&#8217;s basically something that matches anything. 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As stated in the comments, a pointer to an empty interface doesn&#8217;t really make sense as a pointer already matches an empty interface since everything matches an empty interface. To make your code work, you should remove the interface wrapper around ... 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