implicit | 易学教程

Scala Functional Literals with Implicits

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问题 Forgive me if this has already been asked elsewhere. I have a Scala syntax question involving function-values and implicit parameters. I'm comfortable using implicits with Scala's currying feature. For instance if I had a sum function and wanted to make the second argument an implicit: scala> def sum(a: Int)(implicit b: Int) = a + b sum: (a: Int)(implicit b: Int)Int Is there a way to do this using the function-value syntax? Ignoring the implicit for a moment, I typically write curried

Implicit keyword before a parameter in anonymous function in Scala

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I understand implicit parameters and implicit conversions in Scala but I saw this for the first time today: the implicit keyword in front of a parameter in an anonymous function: Action { implicit request => Ok("Got request [" + request + "]") } What does the implicit keyword do here? Are there resources on the web that describes more on what the use case is? There are two distinct features here. First, request isn't really an argument in a method invocation. It's the argument of an anonymous function. The anonymous function itself is the argument of the method invocation. Second, declaring an

Get companion object of class by given generic type Scala

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问题 What I am trying to do is to make a function that would take a generic class and use a static method in it (sorry for Java language, I mean method of its companion object). trait Worker {def doSth: Unit} class Base object Base extends Worker // this actually wouldn't work, just to show what I'm trying to achieve def callSthStatic[T that companion object is <: Worker](implicit m: Manifest[T]) { // here I want to call T.doSth (on T object) m.getMagicallyCompanionObject.doSth } Any ideas? 回答1: I

explicit and implicit c#

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问题 I'm new to C# and learning new words. I find it difficult to understand what's the meaning of these two words when it comes to programming c#. I looked in the dictionary for the meaning and here's what I got: Implicit "Something that is implicit is expressed in an indirect way." "If a quality or element is implicit in something, it is involved in it or is shown by it;" Explicit "Something that is explicit is expressed or shown clearly and openly, without any attempt to hide anything" "If you

Implicit return values in Ruby

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问题 I am somewhat new to Ruby and although I find it to be a very intuitive language I am having some difficulty understanding how implicit return values behave. I am working on a small program to grep Tomcat logs and generate pipe-delimited CSV files from the pertinent data. Here is a simplified example that I'm using to generate the lines from a log entry. class LineMatcher class << self def match(line, regex) output = "" line.scan(regex).each do |matched| output << matched.join("|") << "\n"

ReSharper and var [duplicate]

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Possible Duplicate: Why does ReSharper want to use 'var' for everything? I have ReSharper 4.5 and have found it invaluable so far but I have a concern; It seems to want to make every variable declaration implicit (var). As a relatively new developer, how much should I trust ReSharper when it comes to this? Take the below code snippet from a method that Paints Tab Headers. TabPage currentTab = tabCaseNotes.TabPages[e.Index]; Rectangle itemRect = tabCaseNotes.GetTabRect(e.Index); SolidBrush fillBrush = new SolidBrush(Color.Linen); SolidBrush textBrush = new SolidBrush(Color.Black); StringFormat

Why do members of a static class need to be declared as static? Why isn't it just implicit?

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Obviously there can't be an instance member on a static class, since that class could never be instantiated. Why do we need to declare members as static? I get asked questions like this all the time. Basically the question boils down to "when a fact about a declared member can be deduced by the compiler should the explicit declaration of that fact be (1) required, (2) optional, or (3) forbidden?" There's no one easy answer. Each one has to be taken on a case-by-case basis. Putting "static" on a member of a static class is required. Putting "new" on a hiding, non-overriding method of a derived

Why does this explicit call of a Scala method allow it to be implicitly resolved?

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问题 Why does this code fail to compile, but compiles successfully when I uncomment the indicated line? (I'm using Scala 2.8 nightly). It seems that explicitly calling string2Wrapper allows it to be used implicitly from that point on. class A { import Implicits.string2Wrapper def foo() { //string2Wrapper("A") ==> "B" // <-- uncomment } def bar() { "A" ==> "B" "B" ==> "C" "C" ==> "D" } object Implicits { implicit def string2Wrapper(s: String) = new Wrapper(s) class Wrapper(s: String) { def ==>(s2:

How does SQL Server decide format for implicit datetime conversion?

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问题 declare @str_datetime varchar(50) set @str_datetime='30-04-2012 19:01:45' -- 30th April 2012 declare @dt_datetime datetime select @dt_datetime=@str_datetime This is giving following error: Msg 242, Level 16, State 3, Line 4 The conversion of a varchar data type to a datetime data type resulted in an out-of-range value. My question is how SQL Server decides which format to use for implicit datetime conversion? 回答1: This can depend on a variety of factors - the operating system's regional

What are type classes in Scala useful for?

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As I understand from this blog post "type classes" in Scala is just a "pattern" implemented with traits and implicit adapters. As the blog says if I have trait A and an adapter B -> A then I can invoke a function, which requires argument of type A , with an argument of type B without invoking this adapter explicitly. I found it nice but not particularly useful. Could you give a use case/example, which shows what this feature is useful for ? One use case, as requested... Imagine you have a list of things, could be integers, floating point numbers, matrices, strings, waveforms, etc. Given this