如何在freemarker中将null设置为变量 [英] How to set null to a variable in freemarker

问题描述

在任何问题上我都找不到与此相关的任何东西，这确实很基本，但是我无法弄清楚.

I can't find anything related to this on any question, and it is something really basic, but I can't figure it out.

所以我的问题是我不知道如何在freemarker中将null设置为变量. 示例:

So my problem is that I don't know how to set null to a variable in freemarker. Example:

${hi!"bye"}          <#-- Prints "bye" because hi is undefined -->
<#assign hi="hi">    <#-- Sets a value to the var hi -->
${hi!"bye"}          <#-- Prints "hi" because hi has a value -->
<#assign hi=null>    <#-- This does not work but is what I am looking for -->
${hi!"bye"}          <#-- I want it to print "bye" because hi should be undefined -->

我有这个问题，因为如果特定项目的某些逻辑通过验证，我会遍历一个列表并设置一个var，然后检查该var是否存在，但是如果第一个项目创建了var，那么我将设置var列表中其余项目.

I have this problem because I iterate over a list and set a var if some logic to the specific item validates, and then check if the var exists, but if the first item creates the var, then I will have the var set for the rest of the items in the list.

推荐答案

不，没有"unssign"，在FreeMarker中也没有null的概念(至少到2.4.0，但这还是很遥远).它只有缺失的变量(从技术上讲可能是null，也许根本不存在)和那些在那里.我真的不明白为什么您需要这样做.您可以显示这种情况的简化示例吗?

No, there's no "unassign", nor the concept of null exists in FreeMarker (until 2.4.0 at least, but that's far away anyway). It only have missing variables (maybe technically a null, maybe doesn't exist at all) and those that are there. I don't really get why is that needed in your case. Can you show a simplified example of the situation?

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