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最接近的c等价于f匹配表达式?

guard-clause f# casting c#

Greg Beech · 技术社区 · 15 年前

我的很多类都是由不同类型的知名但无序对象组成的容器,例如,容器可能看起来如下:

public class Container
{
    public A A { get; private set; }
    public B B { get; private set; }
    public C C { get; private set; }

    public bool StoreIfKnown(object o)
    {
        // TODO...
    }
}

所以如果 o 属于类型 A 它应该存储在 一 性质、类型 B 在 B 财产等。

在F中 StoreIfKnown 方法可以写如下(请原谅语法错误,我的f不太好,而且很粗糙):

match o with
| ?: A a -> A <- a; true
| ?: B b -> B <- b; true
| ?: C c -> C <- c; true
| _ -> false

但在c中,唯一的方法似乎是相当冗长的:

if (o is A)
{
    this.A = (A)o;
    return true;
}

if (o is B)
{
    this.B = (B)o;
    return true;
}

// etc.

return false;

我可以用 as 关键字以避免更快但更详细的测试/转换模式。

用C语言做这个有什么优雅的方法吗?

5 回复 | 直到 8 年前

Brian 15 年前

o.Match<A>( a => { this.A = a; return true; } )
 .Match<B>( b => { this.B = b; return true; } )
 .Else( () => { return false; } )

http://blogs.msdn.com/lucabol/archive/2008/07/15/a-c-library-to-write-functional-code-part-v-the-match-operator.aspx

Juliet 15 年前

if (o is {DataType})
{
    {Property} = ({DataType})o;
    return true;
}

public class Container
{
    public A A { get; private set; }
    public B B { get; private set; }
    public C C { get; private set; }

    private bool TestProp<T>(object o, Action<T> f)
    {
        if (o is T)
            return false;

        f((T)o);
        return true;
    }

    public bool StoreIfKnown(object o)
    {
        return
            TestProp<A>(o, x => A = x) ||
            TestProp<B>(o, x => B = x) ||
            TestProp<C>(o, x => C = x) ||
            false;
    }
}

    private bool TestProp<T>(T o, Action<T> f)
    {
        if (o == null)
            return false;

        f(o);
        return true;
    }

    public bool StoreIfKnown(object o)
    {
        return
            TestProp(o as A, x => A = x) ||
            TestProp(o as B, x => B = x) ||
            TestProp(o as C, x => C = x) ||
            false;
    }

Community CDub 8 年前

Brian's answer

C IsActive true

var stored = Match.Against(o)
    .When<A>().Then(a => { this.A = a; return true; })
    .When<B>().Then(b => { this.B = b; return true; })
    .When<C>(c => c.IsActive).Then(c => { this.C = c; return true; })
    .Otherwise(a => false);

flq 15 年前

here

Tomasz MaczyÅski 8 年前

there is a limited support for pattern matching Visual Studio â15â Preview 4

public class Container
{
    public A A { get; private set; }
    public B B { get; private set; }
    public C C { get; private set; }

    public bool StoreIfKnown(object obj)
    {
        switch (obj)
        {
            case A a:
                this.A = a
                // I don't put "break" because I'm returning value from a method
                return true;
            case B b:
                this.B = b
                return true;
            case C c:
                this.C = c
                return true;
            default:
                WriteLine("<other>");
                return false;
        }
    }
}