[英]Generic functions and ref returns in C# 7.0
Is it possible to use the ref returns feature in C# 7.0 define a generic function that can do both comparison and update of a field in two instances of an Object? 是否可以在C#7.0中使用ref returns功能定义一个泛型函数,它可以在Object的两个实例中同时进行字段的比较和更新? I am imagining something like this:
我想象的是这样的:
void UpdateIfChanged<TClass, TField>(TClass c1, TClass c2, Func<TClass, TField> getter)
{
if (!getter(c1).Equals(getter(c2))
{
getter(c1) = getter(c2);
}
}
Example intended usage: 用途示例:
Thing thing1 = new Thing(field1: 0, field2: "foo");
Thing thing2 = new Thing(field1: -5, field2: "foo");
UpdateIfChanged(thing1, thing2, (Thing t) => ref t.field1);
UpdateIfChanged(thing1, thing2, (Thing t) => ref t.field2);
Is there any way to specify a Func type or any kind of generic type restriction that would make this valid by requiring that getter return a reference? 有没有办法指定一个Func类型或任何类型的泛型类型限制,通过要求getter返回引用来使其有效? I tried
Func<TClass, ref TField>
, but it doesn't appear to be valid syntax. 我尝试了
Func<TClass, ref TField>
,但它似乎不是有效的语法。
You won't be able to use Func
, because it doesn't return the result by reference. 您将无法使用
Func
,因为它不会通过引用返回结果。 You'll need to create a new delegate that uses a ref return: 您需要创建一个使用ref return的新委托:
public delegate ref TResult RefReturningFunc<TParameter, TResult>(TParameter param);
Then changing your function to use that delegate is enough for it to work: 然后更改您的函数以使用该委托就足以使其工作:
public static void UpdateIfChanged<TClass, TField>(TClass c1, TClass c2, RefReturningFunc<TClass, TField> getter)
{
if (!getter(c1).Equals(getter(c2)))
{
getter(c1) = getter(c2);
}
}
Note that a property cannot be returned by reference. 请注意,不能通过引用返回属性。 You could return a field by reference, or any other variable , but a property is not a variable.
您可以通过引用或任何其他变量返回字段 ,但属性不是变量。
You need to declare your own delegate type for it. 您需要为它声明自己的委托类型。 For example:
例如:
using System;
public class Thing
{
public int field1;
public string field2;
}
public delegate ref TOutput FuncRef<TInput, TOutput>(TInput input);
public class Test
{
public static void Main()
{
Thing thing1 = new Thing { field1 = 0, field2 = "foo" };
Thing thing2 = new Thing { field1 = -5, field2= "foo" };
UpdateIfChanged(thing1, thing2, (Thing t) => ref t.field1);
UpdateIfChanged(thing1, thing2, (Thing t) => ref t.field2);
}
static void UpdateIfChanged<TInput, TOutput>(TInput c1, TInput c2, FuncRef<TInput, TOutput> getter)
{
if (!getter(c1).Equals(getter(c2)))
{
getter(c1) = getter(c2);
}
}
}
(Note the use of "field" instead of "property" everywhere.) (注意到处使用“field”而不是“property”。)
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