[英]what is wrong with this using generic implicit operator?
如果我在非通用生成器类中使用隐式运算符,则一切正常:
public class ReligionBuilder
{
private Religion _religion;
public ReligionBuilder()
{
_religion = new Religion(){//some codes}
}
public ReligionBuilder AddToRepository()
{
Repository<Religion>.Add(_religion);
return this;
}
public Religion Build()
{
return _religion;
}
public static implicit operator Religion(ReligionBuilder _builder)
{
return _builder.Build();
}
}
我可以使用它:
Religion religion=new ReligionBuilder().AddToRepository();
但是如果此运算符在通用类中,那是错误的:
public abstract class DataTestBuilderBase<T> : IDataTestBuilder<T>
{
protected T TestData { get; set; }
public virtual T Build()
{
return TestData;
}
public abstract IDataTestBuilder<T> AddToRepository();
public abstract IDataTestBuilder<T> WithDefault();
public static implicit operator T(DataTestBuilderBase<T> builder)
{
return builder.Build();
}
}
public class PersonDataTestBuilder : DataTestBuilderBase<Person>
{
private Person _person;
public PersonDataTestBuilder()
{
//some codes
}
public override IDataTestBuilder<Person> AddToRepository()
{
//some codes
return this;
}
}
用法:
PersonDataTestBuilder _testBuilder = new PersonDataTestBuilder();
Person person = _testBuilder.AddToRepository();
错误是:无法将IDataTestBuilder转换为Person
问题是什么?
AddToRepository
只返回IDataTestBuilder<Person>
(在编译时返回类型而言) -而且也从没有隐式转换Person
。 如果将抽象方法的返回类型更改为DataTestBuilderBase<T>
则它应该可以工作-尽管坦率地说,我还是不想使用DataTestBuilderBase<T>
式转换。 我通常对提供隐式转换非常谨慎-就像我相信的那样,它们通常会使代码不清楚。
无论如何,您是否真的应该在构建器上提供AddToRepository
? 对于构建者来说,这感觉像是不适当的操作-我期望:
Person person = new PersonBuilder { /* properties */ }
.Build()
.AddToRepository();
编辑:只是为了显示我的意思,关于更改AddToRepository
的返回类型,这是一个简短而完整的程序来演示。 工作正常。
using System;
public abstract class BuilderBase<T>
{
public abstract T Build();
public abstract BuilderBase<T> AddToRepository();
public static implicit operator T(BuilderBase<T> builder)
{
return builder.Build();
}
}
public class TestBuilder : BuilderBase<string>
{
public override string Build()
{
return "Built by Build()";
}
public override BuilderBase<string> AddToRepository()
{
return this;
}
}
class Program
{
static void Main(string[] args)
{
string x = new TestBuilder().AddToRepository();
Console.WriteLine(x);
}
}
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