我想拥有一个方法 def getInstance[T](dataStr: String): Option[T] = {
T match {
case typeOf[String] => Some(dataStr) // if type of T is String
case typeOf[Integer] => Some(dataStr.toInt) // if type of T is Integer
case typeOf[Boolean] => Some(dataStr.toBoolean) // if type of T is Boolean
case _ => throw new NoSuchElementException()
}
}
，该方法需要一个字符串值并返回一个对象实例，该实例在方法签名中定义为通用
create table t1 (tkey integer, val nvarchar(20) )
create table t2 (tkey integer, val nvarchar(20) )
insert into t1 (tkey, val) values (1, 'abc' )
insert into t1 (tkey, val) values (2, 'efgh' )
insert into t1 (tkey, val) values (3, 'xyz' )
insert into t2 (tkey, val) values (1, 'abc' )
insert into t2 (tkey, val) values (2, ' efgh' )
insert into t2 (tkey, val) values (3, 'xy z' )
select t1.val, t2.val, patindex( t1.val, t2.val )
from t1, t2
where t1.tkey = t2.tkey
如何在Scala中编写相同的文字？
Scala版本：2.11
答案 0 :(得分：5)
类型类可能是最好的解决方案。
/*! normalize.css v8.0.1 | MIT License | github.com/necolas/normalize.css */
/* Document
========================================================================== */
/**
* 1. Correct the line height in all browsers.
* 2. Prevent adjustments of font size after orientation changes in iOS.
*/
html {
line-height: 1.15;
/* 1 */
-webkit-text-size-adjust: 100%;
/* 2 */ }
/* Sections
========================================================================== */
/**
* Remove the margin in all browsers.
*/
body {
margin: 0; }
/**
* Render the `main` element consistently in IE.
*/
main {
display: block; }
/**
* Correct the font size and margin on `h1` elements within `section` and
* `article` contexts in Chrome, Firefox, and Safari.
*/
h1 {
font-size: 2em;
margin: 0.67em 0; }
/* Grouping content
========================================================================== */
/**
* 1. Add the correct box sizing in Firefox.
* 2. Show the overflow in Edge and IE.
*/
hr {
box-sizing: content-box;
/* 1 */
height: 0;
/* 1 */
overflow: visible;
/* 2 */ }
/**
* 1. Correct the inheritance and scaling of font size in all browsers.
* 2. Correct the odd `em` font sizing in all browsers.
*/
pre {
font-family: monospace, monospace;
/* 1 */
font-size: 1em;
/* 2 */ }
/* Text-level semantics
========================================================================== */
/**
* Remove the gray background on active links in IE 10.
*/
a {
background-color: transparent; }
/**
* 1. Remove the bottom border in Chrome 57-
* 2. Add the correct text decoration in Chrome, Edge, IE, Opera, and Safari.
*/
abbr[title] {
border-bottom: none;
/* 1 */
text-decoration: underline;
/* 2 */
text-decoration: underline dotted;
/* 2 */ }
/**
* Add the correct font weight in Chrome, Edge, and Safari.
*/
b,
strong {
font-weight: bolder; }
/**
* 1. Correct the inheritance and scaling of font size in all browsers.
* 2. Correct the odd `em` font sizing in all browsers.
*/
code,
kbd,
samp {
font-family: monospace, monospace;
/* 1 */
font-size: 1em;
/* 2 */ }
/**
* Add the correct font size in all browsers.
*/
small {
font-size: 80%; }
/**
* Prevent `sub` and `sup` elements from affecting the line height in
* all browsers.
*/
sub,
sup {
font-size: 75%;
line-height: 0;
position: relative;
vertical-align: baseline; }
sub {
bottom: -0.25em; }
sup {
top: -0.5em; }
/* Embedded content
========================================================================== */
/**
* Remove the border on images inside links in IE 10.
*/
img {
border-style: none; }
/* Forms
========================================================================== */
/**
* 1. Change the font styles in all browsers.
* 2. Remove the margin in Firefox and Safari.
*/
button,
input,
optgroup,
select,
textarea {
font-family: inherit;
/* 1 */
font-size: 100%;
/* 1 */
line-height: 1.15;
/* 1 */
margin: 0;
/* 2 */ }
/**
* Show the overflow in IE.
* 1. Show the overflow in Edge.
*/
button,
input {
/* 1 */
overflow: visible; }
/**
* Remove the inheritance of text transform in Edge, Firefox, and IE.
* 1. Remove the inheritance of text transform in Firefox.
*/
button,
select {
/* 1 */
text-transform: none; }
/**
* Correct the inability to style clickable types in iOS and Safari.
*/
button,
[type="button"],
[type="reset"],
[type="submit"] {
-webkit-appearance: button; }
/**
* Remove the inner border and padding in Firefox.
*/
button::-moz-focus-inner,
[type="button"]::-moz-focus-inner,
[type="reset"]::-moz-focus-inner,
[type="submit"]::-moz-focus-inner {
border-style: none;
padding: 0; }
/**
* Restore the focus styles unset by the previous rule.
*/
button:-moz-focusring,
[type="button"]:-moz-focusring,
[type="reset"]:-moz-focusring,
[type="submit"]:-moz-focusring {
outline: 1px dotted ButtonText; }
/**
* Correct the padding in Firefox.
*/
fieldset {
padding: 0.35em 0.75em 0.625em; }
/**
* 1. Correct the text wrapping in Edge and IE.
* 2. Correct the color inheritance from `fieldset` elements in IE.
* 3. Remove the padding so developers are not caught out when they zero out
* `fieldset` elements in all browsers.
*/
legend {
box-sizing: border-box;
/* 1 */
color: inherit;
/* 2 */
display: table;
/* 1 */
max-width: 100%;
/* 1 */
padding: 0;
/* 3 */
white-space: normal;
/* 1 */ }
/**
* Add the correct vertical alignment in Chrome, Firefox, and Opera.
*/
progress {
vertical-align: baseline; }
/**
* Remove the default vertical scrollbar in IE 10+.
*/
textarea {
overflow: auto; }
/**
* 1. Add the correct box sizing in IE 10.
* 2. Remove the padding in IE 10.
*/
[type="checkbox"],
[type="radio"] {
box-sizing: border-box;
/* 1 */
padding: 0;
/* 2 */ }
/**
* Correct the cursor style of increment and decrement buttons in Chrome.
*/
[type="number"]::-webkit-inner-spin-button,
[type="number"]::-webkit-outer-spin-button {
height: auto; }
/**
* 1. Correct the odd appearance in Chrome and Safari.
* 2. Correct the outline style in Safari.
*/
[type="search"] {
-webkit-appearance: textfield;
/* 1 */
outline-offset: -2px;
/* 2 */ }
/**
* Remove the inner padding in Chrome and Safari on macOS.
*/
[type="search"]::-webkit-search-decoration {
-webkit-appearance: none; }
/**
* 1. Correct the inability to style clickable types in iOS and Safari.
* 2. Change font properties to `inherit` in Safari.
*/
::-webkit-file-upload-button {
-webkit-appearance: button;
/* 1 */
font: inherit;
/* 2 */ }
/* Interactive
========================================================================== */
/*
* Add the correct display in Edge, IE 10+, and Firefox.
*/
details {
display: block; }
/*
* Add the correct display in all browsers.
*/
summary {
display: list-item; }
/* Misc
========================================================================== */
/**
* Add the correct display in IE 10+.
*/
template {
display: none; }
/**
* Add the correct display in IE 10.
*/
[hidden] {
display: none; }
body {
font: 100% Helvetica, sans-serif;
color: #333; }
这将对trait FromString[T] {
def apply(s: String): T
}
object FromString {
implicit object IntString extends FromString[Int] {
def apply(s: String) = s.toInt
}
implicit object DoubleString extends FromString[Double] {
def apply(s: String) = s.toDouble
}
implicit object BooleanString extends FromString[Boolean] {
def apply(s: String) = s.toBoolean
}
}
def getInstance[T](dataStr: String)(implicit from: FromString[T]): Option[T] =
Some(from(dataStr))
val a = getInstance[Int]("1")
val b = getInstance[Double]("1.0")
val c = getInstance[Boolean]("true")
的有效类型进行编译时检查，并返回适当的getInstance类型。
答案 1 :(得分：2)
您可以在scala中使用模式匹配，从而优雅地解决该问题。
def getInstance[T >: Any](dataStr: String, myType : T) : Option[T] ={
myType match {
case x @ Int => Option(dataStr.toInt)
case x @ Double => Option(dataStr.toDouble)
case x @ Float => Option(dataStr.toFloat)
case _ => throw new NoSuchElementException()
}
}
调用该功能时，
getInstance("1",Int)
getInstance("1",Double)
getInstance("1",Float)
将为您提供
res0: Option[Any] = Some(1)
res1: Option[Any] = Some(1.0)
res2: Option[Any] = Some(1.0)
答案 2 :(得分：1)
我相信您正在尝试使用 Scala的 ClassTag。
import scala.reflect.{ClassTag, classTag}
import scala.util.Try
def getInstance[T](dataStr: String)(implicit T: ClassTag[T]): Option[T] = T match {
case _ if T == classTag[String] => Some(dataStr).flatMap(T.unapply)
case _ if T == classTag[Int] => Try(dataStr.toInt).toOption.flatMap(T.unapply)
case _ if T == classTag[Long] => Try(dataStr.toLong).toOption.flatMap(T.unapply)
case _ if T == classTag[Float] => Try(dataStr.toFloat).toOption.flatMap(T.unapply)
case _ if T == classTag[Double] => Try(dataStr.toDouble).toOption.flatMap(T.unapply)
case _ if T == classTag[Boolean] => Try(dataStr.toBoolean).toOption.flatMap(T.unapply)
case _ => None
}