option | 易学教程

Why is the use of Maybe/Option not so pervasive in Clojure?

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Why does Clojure, despite such an emphasis on functional paradigm, not use the Maybe / Option monad to represent optional values? The use of Option is quite pervasive in Scala, a functional programming language I use regularly. Clojure is not statically typed, so doesn't need the strict this/that/whatever type declarations that are necessary in haskell (and, I gather, Scala). If you want to return a string, you return a string; if you return nil instead, that's okay too. "Functional" does not correspond exactly to "strict compile-time typing". They are orthogonal concepts, and Clojure chooses

前端基础之BOM和DOM

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前端基础之BOM和DOM 1 | 0 前戏到目前为止，我们已经学过了JavaScript的一些简单的语法。但是这些简单的语法，并没有和浏览器有任何交互。也就是我们还不能制作一些我们经常看到的网页的一些交互，我们需要继续学习BOM和DOM相关知识。 JavaScript分为 ECMAScript，DOM，BOM。 BOM（Browser Object Model）是指浏览器对象模型，它使 JavaScript 有能力与浏览器进行“对话”。 DOM （Document Object Model）是指文档对象模型，通过它，可以访问HTML文档的所有元素。 Window对象是客户端JavaScript最高层对象之一，由于window对象是其它大部分对象的共同祖先，在调用window对象的方法和属性时，可以省略window对象的引用。例如：window.document.write()可以简写成：document.write()。 1 | 1 window对象所有浏览器都支持 window 对象。它表示浏览器窗口。 *如果文档包含框架（frame 或 iframe 标签），浏览器会为 HTML 文档创建一个 window 对象，并为每个框架创建一个额外的 window 对象。 *没有应用于 window 对象的公开标准，不过所有浏览器都支持该对象。所有 JavaScript 全局对象

Opencart - Customer uploads different files to one product with different responses from the site

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I am using Opencart 1.5.6 and I have two file upload options for one product. One option is an image and the other is a video. I am setting it up to show a preview of the image once they upload. In catalog/controller/product/product.php under public function upload() I have changed the code as follows to get a thumbnail image and change the success message: if (!$json && is_uploaded_file($this->request->files['file']['tmp_name']) && file_exists($this->request->files['file']['tmp_name'])) { $file = basename($filename) . '.' . md5(mt_rand()); // Hide the uploaded file name so people can not link

年月日日期选择问题

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<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title></title> <style type="text/css"> div { height: 300px; width: 300px; margin: 0px auto; } </style> </head> <body> <div> <select id="year" onChange="a()"> <option value="0" selected></option> <!--<option value="1986">1986</option> <option value="1987">1987</option> <option value="1988">1988</option> <option value="1989">1989</option> <option value="1990">1990</option> <option value="1991">1991</option> <option value="1992">1992</option> <option value="1993">1993</option> <option value="1994">1994</option> <option value="1995">1995<

Override option in CMake subproject

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问题 I'm trying to reuse the CMakeLists.txt of a third-party project whose source I don't want to change (expat, to be exact). I've added the project as a subproject of the top level using add_subdirectory . This works but now I would like to set the value of some of the subproject's option s in the top level CMakeLists.txt . How do I do this? 回答1: See the similar question with a good answer. Answer in short: SET(SOME_EXPAT_OPTION OFF CACHE BOOL "Use some expat option") 回答2: If the sub-project

element-ui el-select 多选单选切换报错问题

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项目需求后台表单是前台自建的控件自然也要自建自然就有各种选项其中选择框就有单选多选选项项目使用的element-ui 自然就用的el-select 由于数据库并没有类似数组的字段选择框使用varchar 而el-select多选时却需要使用数组所以在编辑时需要将值转成数组再赋值给el-select的value <template> <el-select :value="data" @change="val => $emit('input', String(val))" :disabled="control.disabled == '1'" :multiple="control.multiple == '1'" :allow-create="control.allow_create == '1'" :style="css" :size="size" filterable default-first-option clearable > <el-option v-for="option in options" :key="option.value" :label="option.label" :value="option.value"> <slot :option="option"></slot> <!-- <component v-if="slotsEx" :is=

thymeleaf / select option list遍历循环

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<option th:each="car,userStat:${carList}" th:value="${car.carId}" th:text="${car.name}"></option> <div class="form-group"> <label for="parentId" class="col-sm-2 control-label">车</label> <div class="col-sm-8"> <select name="carIs" id="carId" class="form-control1"> <option th:each="car,userStat:${carList}" th:value="${car.carId}" th:text="${car.name}"></option> </select> </div> </div> 选中的情况下返回的map中有2个值一个是carList 一个是car <option th:each="list,userStat:${carList}" th:value="${list.carId}" th:text="${car.name}" th:selected="${list.carId == car.carId}"></option> 参考地址 https://blog.csdn.net

HTML 表单 / HTML5 表单元素datalist

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<form> 属性的列表：属性描述 accept-charset 规定在被提交表单中使用的字符集（默认：页面字符集）。 action 规定向何处提交表单的地址（URL）（提交页面）。 autocomplete 规定浏览器应该自动完成表单（默认：开启）。 enctype 规定被提交数据的编码（默认：url-encoded）。 method 规定在提交表单时所用的 HTTP 方法（默认：GET）。 name 规定识别表单的名称（对于 DOM 使用：document.forms.name）。 novalidate 规定浏览器不验证表单。 target 规定 action 属性中地址的目标（默认：_self）。 <select> 元素（下拉列表） <select name="cars"> 　　<option value="volvo">Volvo</option> 　　<option value="saab">Saab</option> 　　<option value="fiat">Fiat</option> 　　<option value="audi">Audi</option> </select> <option> 元素定义待选择的选项。列表通常会把首个选项显示为被选选项。您能够通过添加 selected 属性来定义预定义选项。 <option value="fiat"

jQuery simulate click event on select option

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问题 I have a select menu that triggers an AJAX request once one of the options has been clicked. I need to trigger a click event on the relevant option from a link. So I have code similar to the below, and although it changes the value of the select, it doesn't simulate a click: $('#click').click(function(){ var value = $(this).attr("rel"); $('#select').val(value); return false; }); <select id="select" name="select"> <option>Select...</option> <option value="1">Option 1</option> <option value="2"

Mapping a FunctionalJava Option<Type> with Hibernate

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I have a hibernate-mapped Java object, JKL , which is full of a bunch of normal hibernate-mappable fields (like strings and integers). I'm added a new embedded field to it (which lives in the same table -- not a mapping), asdf , which is a fj.data.Option<ASDF> . I've made it an option to make it clear that this field may not actually contain anything (as opposed to having to handle null every time I access it). How do I set up the mapping in my JKL.hbm.xml file? I'd like hibernate to automatically convert a null in the database to a none of fj.data.Option<ASDF> when it retrieves the object. It

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