在Drools中，什么是Mvel方言?

问题描述

我是Drools的新手.我正在创建规则，但出现编译时错误

I am new to Drools. I am creating a rule but I get a compile time error

我尝试检查Jboss示例，其中使用了方言奇迹" .它编译了.我不了解方言.那么什么是dialect=mvel?

I've tried to check with Jboss examples, where they use dialect "mvel". It compiled. I didn't understand about dialect. So what is dialect=mvel?

推荐答案

mvel或 MVFLEX表达式语言具有丰富的语法，其中许多语法允许使用更简洁明了的代码(且比java少的命令性)，例如

mvel, or the MVFLEX Expression Language has a rich syntax, many of which allow for more concise and expressive code (and less imperative) than java, e.g.

• 用于get() ters/set() ters(例如封装私有字段)的简写，可以使用另一种property样式语法(类似于.Net中的VB或C#属性)

• Shorthand for get()ters / set()ters (e.g. encapsulating private fields) to be accessed in an alternative property style syntax (similar to VB or C# properties in .Net)

即.代替

myObject.setSomeField("SomeValue");
int x = myObject.getSomeIntField();

您可以使用语法(也请注意细微的大小写开关):

You can use the syntax (note the subtle capitalization switch as well):

myObject.someField = "SomeValue"
x = myObject.someIntField // Type inferrence

• return语句是可选的(在许多功能语言(如Scala中都可以找到)的约定)和分号一样，除非每行有多个语句:
• The return statement is optional (a convention found in many functional languages like Scala), as is the semi-colon, unless you have multiple statements per line:

x  // i.e. return x;

• 按顺序创建速记数组和建立索引

foos = {2, 4, 6, 8, 10}
foos[3] // foos.get(3)

• 类似地用于地图(词典)

bars = ["a" : "Apple", "b" : "Basket"] // Hashmap, with put
bars["a"]
bars.a // Similar to dynamically typed object e.g. in javascript, if key is a string.

• 空安全导航运算符(例如Rosyln中的空条件运算符)

foo.?bar.baz // if (foo.bar != null) { return foo.bar.baz; } else { return null; }

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