blocks|key|1381659|text|这样如何：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1381660|Welcome+to+Scala+version+2.8.0.r19650-b20091114020153+(Java+HotSpot(TM)+Client+VM,+Java+1.6.0_17).
Type+in+expressions+to+have+them+evaluated.
Type+:help+for+more+information.

scala>+def+optfToPf[X,R](f:+X+=>+Option[R]):+PartialFunction[X,R]+=+x+=>+f(x)+match+{
+++++%7C+++++case+Some(r)+=>+r
+++++%7C+}
optfToPf:+[X,R](f:+(X)+=>+Option[R])PartialFunction[X,R]

scala>|code-block|syntax|javascript|1381661|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

How about this:

<pre><code>Welcome to Scala version 2.8.0.r19650-b20091114020153 (Java HotSpot(TM) Client VM, Java 1.6.0_17).
Type in expressions to have them evaluated.
Type :help for more information.

scala&gt; def optfToPf[X,R](f: X =&gt; Option[R]): PartialFunction[X,R] = x =&gt; f(x) match {
 | case Some(r) =&gt; r
 | }
optfToPf: [X,R](f: (X) =&gt; Option[R])PartialFunction[X,R]

scala&gt;
</code></pre>

blocks|key|1381678|text|我想你可以手动覆盖apply和isDefinedAt，但我会按照你觉得难看的方式来做。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1381679|def+optfToPf[X,R](f:+X+=>+Option[R])+=+new+PartialFunction[X,R]+{
++def+apply(x:+X):+R+=+f(x).get
++def+isDefinedAt(x:+X):+Boolean+=+f(x)+!=+None
}|code-block|syntax|javascript|1381680|测试：|1381681|scala>+val+map+=+Map(1+->+2)
map:+scala.collection.immutable.Map[Int,Int]+=+Map(1+->+2)

scala>+map(1)
res0:+Int+=+2

scala>+def+mapOpt(key:+Int)+=+map.get(key)
mapOpt:+(key:+Int)Option[Int]

scala>+mapOpt(1)
res1:+Option[Int]+=+Some(2)

scala>+mapOpt(2)
res2:+Option[Int]+=+None

scala>+val+mapPf+=+optfToPf(mapOpt+_)
mapPf:+java.lang.Object+with+PartialFunction[Int,Int]+=+<function1>

scala>+mapPf.isDefinedAt(2)
res3:+Boolean+=+false

scala>+mapPf.isDefinedAt(1)
res4:+Boolean+=+true

scala>+mapPf(1)
res5:+Int+=+2

scala>+mapPf(2)
java.util.NoSuchElementException:+None.get|1381682|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I suppose you could override apply and isDefinedAt by hand, but I'd do it the way you find ugly.

<pre><code>def optfToPf[X,R](f: X =&gt; Option[R]) = new PartialFunction[X,R] {
 def apply(x: X): R = f(x).get
 def isDefinedAt(x: X): Boolean = f(x) != None
}
</code></pre>

Testing:

<pre><code>scala&gt; val map = Map(1 -&gt; 2)
map: scala.collection.immutable.Map[Int,Int] = Map(1 -&gt; 2)

scala&gt; map(1)
res0: Int = 2

scala&gt; def mapOpt(key: Int) = map.get(key)
mapOpt: (key: Int)Option[Int]

scala&gt; mapOpt(1)
res1: Option[Int] = Some(2)

scala&gt; mapOpt(2)
res2: Option[Int] = None

scala&gt; val mapPf = optfToPf(mapOpt _)
mapPf: java.lang.Object with PartialFunction[Int,Int] = &lt;function1&gt;

scala&gt; mapPf.isDefinedAt(2)
res3: Boolean = false

scala&gt; mapPf.isDefinedAt(1)
res4: Boolean = true

scala&gt; mapPf(1)
res5: Int = 2

scala&gt; mapPf(2)
java.util.NoSuchElementException: None.get
</code></pre>

As long as we have a <code>PartialFunction[X,R]</code> it's very easy to convert it to a function returning <code>Option[R]</code>, e.g.

<pre><code>def pfToOptf[X, R](f: PartialFunction[X,R])(x: X) =
 if (f.isDefinedAt(x)) Some(f(x))
 else None
</code></pre>

However, what if the task is opposite: suppose I have a function <code>f</code> getting <code>X</code> as an argument and returning <code>Option[R]</code> as a result. And I want to make a <code>PartialFunction[X,R]</code> out of it. What is the best way?

What I've come up with looks pretty ugly to my taste:

<pre><code>def optfToPf[X,R](f: X =&gt; Option[R]) : PartialFunction[X,R] = {
 object extractor {
 def unapply(x: X): Option[R] = f(x)
 }

 { case extractor(r) =&gt; r }
}
</code></pre>

Is there some better way I missed?

How to convert X => Option[R] to PartialFunction[X,R]

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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只要我们有一个PartialFunction[X,R]，就很容易把它转换成一个返回Option[R]的函数，例如def pfToOptf[X, R](f: PartialFunction[X,R])(x: X) =    if (f.isDefinedAt(x)) Some(f(x))    else None然而，如...

问如何将X => Option[R]转换为PartialFunction[X，R]
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