The dynamic analysis and calculation of expressions are really delicious for flee

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Preface

In many projects, there are often scenarios that require dynamic parsing of expressions and calculations , For example, some automatic approval rules , Or the values of some variables are dynamically calculated during operation through the maintained formula ; Due to scenario requirements , You need to configure the corresponding expression flexibly , Then I hope to calculate the corresponding value according to the maintained expression when necessary ; When I was chatting with my colleagues, I said Flee, I think it works very well , Hurry to share a wave with your friends .

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1. Flee brief introduction

Flee Is a . net Framework's expression parser and evaluator , You can evaluate string expressions at run time ( Such as ：sqrt(a^2 + b^2), among a、b It's a variable. ). Its parsing and computing speed is relatively fast and efficient .

Flee Support Net6.0、Net5.0、Netstandard2.1、Netstandard2.0.

Not much else , Let's go directly to a few examples to experience a wave , For more details, you can go to github Look up ：

github Address ：https://github.com/mparlak/Flee

2. Case presentation

The case is demonstrated through the console , On the installation Flee Bag can .

2.1 Super simple case

There are specific comments in the code , I won't go into details here , The screenshot is as follows ：

The content of this simple expression has been determined , All are computable , No variables .

Application scenarios 1： Expression fixed , A scene calculated directly by splicing the corresponding values .

Application scenarios 2： The expression is not fixed , However, some variable values are marked with special characters during formula maintenance , Then find the marked variable in the form of regular expression , And replace with the corresponding business field value .

Such as ：[a]+[b]+3.14, In this case, the variables marked with brackets can be found through regular expressions , Then we can calculate by replacing the corresponding value with the name of the corresponding intermediate variable .

2.2 Expressions with variables

There are specific comments in the code , I won't go into details here , The screenshot is as follows ：

This form with variables is relatively flexible , It can be configured at will , Just attach values to the corresponding variables during calculation . There may be some questions from my friends , How to adjust variable uncertainty , In fact, in the actual application scenario , You should know the variables that need to be passed in many times , Just dynamically transfer values according to the rules of the formula .

Application scenarios ： It is different from the simple case , No special tag variables are required , Here, you can directly maintain the formula and transfer values normally . This situation is relatively flexible , Corresponding formulas can be configured for related businesses , The last pass is the corresponding variable for calculation , Finally, relevant business processing can be carried out according to the calculated value .

2.3 Expression combination

CalculationEngine You can combine expressions , The calculation engine will use the results of other expressions inside the engine 、 Dependency relationship , Then calculate the combined results in sequence .

Application scenarios ： This is generally used in scenarios with multiple expressions , Is similar to the Excel The same expression in multiple cells in , Every cell has an expression , Then one cell will reference the value calculated by the expression in other cells , Finally, the result .

2.4 spread function

Sometimes computing logic is encapsulated in a project , Just pass in the required value , There is no need for each caller to rewrite the relevant calculation logic ,Flee It also supports the combination of custom functions in expressions , The demonstration is as follows ：

First, write the relevant methods in a class **, The method here must be static 、 Public **, as follows ：

Then you can use it in the expression , as follows ：

2.5 Functions that support variable arguments

It is used in the same way as above , Customize a method , Only the parameters of this method are uncertain , Variable , as follows ：

Use... In expressions ：

2.6 The return value is Boolean Expression of type

In practical application scenarios , Sometimes you just need to get a yes no result , It may not be necessary to calculate a specific value ;

Application scenarios ： This situation is generally used for the requirements of some automatic decision rules , For example, the results of some reports have a range of values for different business types , If it is out of range, it means non-compliance , If you rely on human judgment, it may not be so efficient ; Similar to this case of comparative data , If it is only a simple comparison, it is easy to realize , If it is a more complicated relationship comparison , This method is relatively flexible .

Okay , For the time being, let's talk about how to use it , The pictures in this article already contain all the codes . I will also submit the code later github And code cloud .

summary

The above is just a few simple examples , Specific partners can use it according to business scenarios . If you have a better tool library , Comments are welcome , Learning together .

Focus on “Code Variety industry ”, Study with me .