表达式< Func> T，bool>方法参数

问题描述：

我正在尝试创建一个通用方法来返回表达式的字符串版本:

I'm trying to make a generic method that returns the string version of an expression:

public string GetExpressionString(Expression<Func<T, bool>> expr) where T: class
{
    return exp.Body.ToString();
}

无法解析符号T

如果我将 T 更改为硬编码类型，效果很好.

Works well if I change T to a hard coded type.

我想念什么?

答

您需要将 T 声明为方法的通用类型参数:

You'll need to declare T as a generic type parameter on the method:

public string GetExpressionString<T>(Expression<Func<T, bool>> exp)
    where T: class
{
    return exp.Body.ToString();
}

// call like this
GetExpressionString<string>(s => false);
GetExpressionString((Expression<Func<string, bool>>)(s => false));

或者在父类上:

public class MyClass<T>
    where T: class
{
    public string GetExpressionString(Expression<Func<T, bool>> exp)
    {
        return exp.Body.ToString();
    }
}

// call like this
var myInstance = new MyClass<string>();
myInstance.GetExpressionString(s => false);

进一步阅读:

通用方法(C#编程指南)

表达式< Func> T，bool>方法参数

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