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get end values from lambda expressions method parameters

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青春惊慌失措
青春惊慌失措 2020-12-10 15:48

basically I want to get the values of the parameters of a called method like this:

var x = 1;
var a = 2;
var b = 3;
Do(o => o.Save(x
5条回答
  • 盖世英雄少女心
    盖世英雄少女心 (楼主)
    2020-12-10 16:21

    Here is some code that is designed to work with any expression — in the sense that it doesn’t fundamentally assume that you are passing in a method-call expression. However, it is not complete. You will have to fill in the rest.

    public static IEnumerable ExtractConstants(
        Expression> expression)
{
    return extractConstants(expression);
}
private static IEnumerable extractConstants(Expression expression)
{
    if (expression == null)
        yield break;

    if (expression is ConstantExpression)
        yield return ((ConstantExpression) expression).Value;

    else if (expression is LambdaExpression)
        foreach (var constant in extractConstants(
                ((LambdaExpression) expression).Body))
            yield return constant;

    else if (expression is UnaryExpression)
        foreach (var constant in extractConstants(
                ((UnaryExpression) expression).Operand))
            yield return constant;

    else if (expression is MethodCallExpression)
    {
        foreach (var arg in ((MethodCallExpression) expression).Arguments)
            foreach (var constant in extractConstants(arg))
                yield return constant;
        foreach (var constant in extractConstants(
                ((MethodCallExpression) expression).Object))
            yield return constant;
    }

    else
        throw new NotImplementedException();
}



    For the case that you have mentioned, this already works:
    


    // Prints:
// Jimmy (System.String)
// 1 (System.Int32)
foreach (var constant in Ext.ExtractConstants(
        str => Console.WriteLine("Jimmy", 1)))
    Console.WriteLine("{0} ({1})", constant.ToString(),
                                   constant.GetType().FullName);

    


    For more complex lambda expressions that employ other types of expression nodes, you will have to incrementally extend the above code. Every time you use it and it throws a NotImplementedException, here is what I do:
    


      

    • Open the Watch window in the debugger
      • 

    • Look at the expression variable and its type
      • 

    • Add the necessary code to handle that expression type
      • 

    


    Over time the method will become more and more complete.
    
    
    
             
    
                                                        
    
            
            
    
              
                
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