blocks|key|214521|text|我相信你需要这样定义你的类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|214522|public+class+MyThingConsumer<Thing>+:+ThingConsumer|code-block|syntax|javascript|214523|原因是ThingConsumer在其定义中已经键入了以下内容：where+T+:+IThing|offset|length|style|CODE|214524|现在，您可以调用return+new+MyThingConsumer<T>();。|214525|这又应该与ThingConsumer<T>的预期返回类型相匹配|214526|编辑|BOLD|214527|很抱歉造成混乱，以下是应该起作用的方法：|214528|public+class+MyThingConsumer<T>+:+ThingConsumer<T>+where+T+:+IThing|214529|和|214530|return+new+MyThingConsumer<T>();|214531|entityMap^0|0|0|3|D|V|G|0|8|W|0|5|G|0|0|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@$I|16|J|17|K|L]|$I|18|J|19|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|1A|8|@$I|1B|J|1C|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1D|8|@$I|1E|J|1F|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1G|8|@$I|1H|J|1I|K|S]]|9|@]|A|$]]|$1|T|3|U|5|6|7|1J|8|@]|9|@]|A|$]]|$1|V|3|W|5|D|7|1K|8|@]|9|@]|A|$E|F]]|$1|X|3|Y|5|6|7|1L|8|@]|9|@]|A|$]]|$1|Z|3|10|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|11|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|12|$]]

You need to define your class like this I believe:

<pre><code>public class MyThingConsumer&lt;Thing&gt; : ThingConsumer
</code></pre>

The reason is that <code>ThingConsumer</code> is already typed in its definition with this: <code>where T : IThing</code>

Now, you can make the call <code>return new MyThingConsumer&lt;T&gt;();</code>.

This should in turn match the expected return type of <code>ThingConsumer&lt;T&gt;</code>

EDIT

Sorry for the confusion, here is what should work:

<pre><code>public class MyThingConsumer&lt;T&gt; : ThingConsumer&lt;T&gt; where T : IThing
</code></pre>

and

<pre><code>return new MyThingConsumer&lt;T&gt;();
</code></pre>

blocks|key|2858506|text|如果您将ThingConsumer<T>作为接口而不是抽象类，那么您的代码将按原样工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2858507|public+interface+IThingConsumer<T>+where+T+:+IThing
{
++++string+Name+{+get;+set;+}
}|code-block|syntax|javascript|2858508|编辑|BOLD|2858509|还需要再做一次改变。在ThingConsumerFactory中，强制转换回返回类型IThingConsumer<T>|2858510|return+(IThingConsumer<T>)new+MyThingConsumer();|2858511|entityMap^0|4|G|0|0|0|2|0|B|K|16|H|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|W|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|X|8|@$9|Y|A|Z|B|M]]|D|@]|E|$]]|$1|N|3|O|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|R|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|S|$]]

If you make <code>ThingConsumer&lt;T&gt;</code> an interface rather than an abstract class, then your code will work as is.

<pre><code>public interface IThingConsumer&lt;T&gt; where T : IThing
{
 string Name { get; set; }
}
</code></pre>

Edit 

One more change needed. In <code>ThingConsumerFactory</code>, cast back to the return type <code>IThingConsumer&lt;T&gt;</code>:

<pre><code>return (IThingConsumer&lt;T&gt;)new MyThingConsumer();
</code></pre>

blocks|key|214675|text|编译器在从MyThingConsumer到ThingConsumer<T>的转换中遇到了困难，即使是T:IThing、MyThingConsumer:Thingconsumer<Thing>和Thing:IThing也是如此。对于它来说，这是一个相当多的障碍！|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|214676|如果您使用return+new+MyThingConsumer()+as+ThingConsumer<T>;而不是直接转换，则代码可以正常工作。您知道结果永远不会是null，编译器很高兴，因为它在运行时得到了正确类型的返回值。|214677|编辑：这里是我用来测试的完整代码(用Snippy编写)：|BOLD|214678|public+interface+IThing
{
++++string+Name+{+get;+}
}

public+class+Thing+:+IThing
{
++++public+string+Name+{+get;+set;+}
}

public+abstract+class+ThingConsumer<T>+where+T+:+IThing
{
++++public+string+Name+{+get;+set;+}
}

public+class+MyThingConsumer+:+ThingConsumer<Thing>
{
}

public+static+class+ThingConsumerFactory<T>+where+T+:+IThing
{
++++public+static+ThingConsumer<T>+GetThingConsumer()
++++{
++++++++if+(typeof(T)+==+typeof(Thing))
++++++++{
++++++++++++return+new+MyThingConsumer()+as+ThingConsumer<T>;
++++++++}
++++++++else
++++++++{
++++++++++++return+null;
++++++++}
++++}
}

...

var+thing+=+ThingConsumerFactory<Thing>.GetThingConsumer();
Console.WriteLine(thing);|code-block|syntax|javascript|214679|entityMap|0|LINK|mutability|MUTABLE|url|http://www.csharpindepth.com/Downloads.aspx^0|5|F|L|G|1E|8|1N|10|2O|C|0|5|1D|2A|4|0|0|3|I|6|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1D|8|@$9|1E|A|1F|B|J]]|D|@$9|1G|A|1H|1|1I]]|E|$]]|$1|K|3|L|5|M|7|1J|8|@]|D|@]|E|$N|O]]|$1|P|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|Q|$R|$5|S|T|U|E|$V|W]]]]

The compiler is stumbling over the conversion from <code>MyThingConsumer</code> to <code>ThingConsumer&lt;T&gt;</code> even though <code>T:IThing</code> and <code>MyThingConsumer:Thingconsumer&lt;Thing&gt;</code> and <code>Thing:IThing</code>. Which is quite a few hoops for it to jump through!

The code works if you use <code>return new MyThingConsumer() as ThingConsumer&lt;T&gt;;</code> instead of a direct cast. You know the result will never be <code>null</code>, and the compiler is happy because it is guaranteed a return value of the right type at runtime.

Edit:
Here is the full code I used for testing (in <a href="http://www.csharpindepth.com/Downloads.aspx" rel="nofollow">Snippy</a>):

<pre><code>public interface IThing
{
 string Name { get; }
}

public class Thing : IThing
{
 public string Name { get; set; }
}

public abstract class ThingConsumer&lt;T&gt; where T : IThing
{
 public string Name { get; set; }
}

public class MyThingConsumer : ThingConsumer&lt;Thing&gt;
{
}

public static class ThingConsumerFactory&lt;T&gt; where T : IThing
{
 public static ThingConsumer&lt;T&gt; GetThingConsumer()
 {
 if (typeof(T) == typeof(Thing))
 {
 return new MyThingConsumer() as ThingConsumer&lt;T&gt;;
 }
 else
 {
 return null;
 }
 }
}

...

var thing = ThingConsumerFactory&lt;Thing&gt;.GetThingConsumer();
Console.WriteLine(thing);
</code></pre>

I have the following classes and interfaces:

<pre><code>public interface IThing
{
 string Name { get; }
}

public class Thing : IThing
{
 public string Name { get; set; }
}

public abstract class ThingConsumer&lt;T&gt; where T : IThing
{
 public string Name { get; set; }
}
</code></pre>

Now, I have a factory that will return objects derived from ThingConsumer like:

<pre><code>public class MyThingConsumer : ThingConsumer&lt;Thing&gt;
{
}
</code></pre>

My factory currently looks like this:

<pre><code>public static class ThingConsumerFactory&lt;T&gt; where T : IThing
{
 public static ThingConsumer&lt;T&gt; GetThingConsumer(){
 if (typeof(T) == typeof(Thing))
 {
 return new MyThingConsumer();
 }
 else
 {
 return null;
 }
 }
}
</code></pre>

I'm getting tripped up with this error: <code>Error 1 Cannot implicitly convert type 'ConsoleApplication1.MyThingConsumer' to 'ConsoleApplication1.ThingConsumer&lt;T&gt;'</code>

Anyone know how to accomplish what I'm attempting here?

Thanks!

Chris

Cannot implicitly convert derived type to its base generic type

编译器

我有以下类和接口：public interface IThing{ string Name { get; }}public class Thing : IThing{ public string Name { get; set; }}public abstract class ThingConsumer<T...

问无法将派生类型隐式转换为其基泛型类型
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