无法隐式转换类型' int'到&char;#39;在使用聚合扩展方法时 [英] Cannot implicitly convert type 'int' to 'char' while using Aggregate Extension method

问题描述

尝试反转字符串，但在聚合函数中出现错误

Trying to reverse a string but getting error in Aggregate function

private string Reverse(string strValue)
        {

            char[] chArray = strValue.ToCharArray();
            var reverse = chArray.Reverse();

            var res = reverse.Aggregate((a,b)=>a+b);

            return res.ToString();
        }

无法将类型'int'隐式转换为'char'.存在显式转换(您是否缺少演员表?)那怎么了?

推荐答案

确切地说: a + b 的结果是 int ，但是您需要成为 char .要使其编译，您可以使用:

Exactly as it says: the result of a + b is an int, but you want it to be a char. To get it to compile you can just use:

var res = reverse.Aggregate((a,b)=>(char) (a+b));

...但是我认为这不会满足您的要求.

... but I don't think that will do what you want it to.

我建议您不要以LINQ开头:

I suggest you don't use LINQ for this to start with:

private string Reverse(string strValue)
{
    char[] chArray = strValue.ToCharArray();
    Array.Reverse(chArray);
    return new string(chArray);
}

请注意，此不能正常使用，例如组合字符，代理对等.

Note that this doesn't work properly with things like combining characters, surrogate pairs etc.

如果您真的想使用LINQ，可以使用:

If you really wanted to use LINQ, you could do it with:

private string Reverse(string strValue)
{
    return new string(strValue.Reverse().ToArray());
}

无需调用 Aggregate .如果您真的想要使其变慢并且将字符串连接与 Aggregate (它将是O(n ² ))一起使用，则可以执行此操作像这样:

There's no need to call Aggregate. If you really want to make it slow and use string concatenation with Aggregate (it'll be O(n²)) you can do it like this:

private string Reverse(string strValue)
{
    return strValue.Reverse().Aggregate("", (str, c) => str + c);
}

这里我们提供了一个字符串种子值，因此参数 str 将是字符串，而 + 将是字符串串联，而不是字符 addition .

Here's we've provided a string seed value, so the parameter str will be a string and + will be string concatenation, not character addition.

您可以使用 StringBuilder 使其更高效:

You can make it more efficient using StringBuilder:

private string Reverse(string strValue)
{
    return strValue.Reverse()
                   .Aggregate(new StringBuilder(), (sb, c) => sb.Append(c))
                   .ToString();
}

...但是我仍然不确定是否值得...

... but I'm still not sure it's worth it...

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