根据类型参数在通用方法中调用不同的方法 [英] Call different methods in a generic method based on the type parameter

问题描述

我有几种这样的方法:

public string GetStringValue(string field) { /* ... */ }
public int GetIntValue(string field) { /* ... */ }

现在，我想编写一个具有以下签名的通用方法:

Now I want to write a generic method which has the following signature:

public bool CopyValue<T>(string field, Action<T> copyAction)

根据类型参数，我想使用非泛型方法之一的返回值调用copyAction.我的第一次尝试是

Depending on the type parameter I want to invoke copyAction with the return value of one of the non-generic methods. My first try was

public bool CopyValue<T>(string field, Action<T> copyAction)
{
    if (typeof(T) == typeof(string))
        copyAction((GetStringValue(field));
    else if (typeof(T) == typof(int))
        copyAction(GetIntValue(field));
    else
        return false;

    return true;
}

但是，这甚至无法编译.然后，我尝试将非通用的方法包装在通用的方法中，例如

But this doesn't even compile. I then tried to wrap my non-generic metods in generic ones like

public string GetValue<string>(string field)
{
    return GetStringValue(field);
}

显然也不能编译.

可以做到这一点还是我必须为每种类型显式实现CopyValue?

Can this be done or do i have to explicitly implement CopyValue for each type?

推荐答案

您可以将其用于投射，但这很丑陋:

You can get it to work with casting, but it's ugly:

if (typeof(T) == typeof(string))
{
    copyAction((T)(object) GetStringValue(field));
}

(等)

老实说，这种事情总是以丑陋结束.一种选择是像这样创建Dictionary<Type, Delegate>:

This sort of thing always ends up being fairly ugly, to be honest. One option would be to create a Dictionary<Type, Delegate> like this:

Dictionary<Type, Delegate> fieldExtractors = new Dictionary<Type, Delegate>
{
    { typeof(string), (Func<string, string>) field => GetStringValue(field) },
    { typeof(int), (Func<string, int>) field => GetIntValue(field) },
};

然后您可以使用:

public bool CopyValue<T>(string field, Action<T> copyAction)
{
    Delegate fieldExtractor;
    if (fieldExtractors.TryGetValue(typeof(T), out fieldExtractor))
    {
        var extractor = (Func<string, T>) fieldExtractor;
        copyAction(extractor(field));
        return true;
    }
    return false;
}

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