A conversion from the representation type Repr to a GenTraversableLike[A,Repr].
Returns string formatted according to given format string.
Returns string formatted according to given format string.
Format strings are as for String.format
(@see java.lang.String.format).
A trait which can be used to avoid code duplication when defining extension methods that should be applicable both to existing Scala collections (i.e., types extending
GenTraversableLike) as well as other (potentially user-defined) types that could be converted to a Scala collection type. This trait makes it possible to treat Scala collections and types that can be implicitly converted to a collection type uniformly. For example, one can provide extension methods that work both on collection types and onStrings (Strings do not extendGenTraversableLike, but can be converted toGenTraversableLike)IsTraversableprovides two members:A, which represents the element type of the targetGenTraversableLike[A, Repr]conversion, which provides a way to convert between the type we wish to add extension methods to,Repr, andGenTraversableLike[A, Repr].Usage
One must provide
IsTraversableLikeas an implicit parameter type of an implicit conversion. Its usage is shown below. Our objective in the following example is to provide a generic extension methodmapReduceto any type that extends or can be converted toGenTraversableLike. In our example, this includesString.Here, we begin by creating a class
ExtensionMethodswhich contains ourmapReduceextension method. Note thatExtensionMethodstakes a constructor argumentcollof typeGenTraversableLike[A, Repr], whereArepresents the element type andReprrepresents (typically) the collection type. The implementation ofmapReduceitself is straightforward.The interesting bit is the implicit conversion
withExtensions, which returns an instance ofExtensionMethods. This implicit conversion can only be applied if there is an implicit valuetraversableof typeIsTraversableLike[Repr]in scope. SinceIsTraversableLikeprovides value memberconversion, which gives us a way to convert between whatever type we wish to add an extension method to (in this case,Repr) andGenTraversableLike[A, Repr], we can now convertcollfrom typeReprtoGenTraversableLike[A, Repr]. This allows us to create an instance of theExtensionMethodsclass, which we pass our newGenTraversableLike[A, Repr]to.When the
mapReducemethod is called on some type of which it is not a member, implicit search is triggered. Because implicit conversionwithExtensionsis generic, it will be applied as long as an implicit value of typeIsTraversableLike[Repr]can be found. Given thatIsTraversableLikecontains implicit members that return values of typeIsTraversableLike, this requirement is typically satisfied, and the chain of interactions described in the previous paragraph is set into action. (See theIsTraversableLikecompanion object, which contains a precise specification of the available implicits.)Note: Currently, it's not possible to combine the implicit conversion and the class with the extension methods into an implicit class due to limitations of type inference.
Implementing
IsTraversableLikefor New TypesOne must simply provide an implicit value of type
IsTraversableLikespecific to the new type, or an implicit conversion which returns an instance ofIsTraversableLikespecific to the new type.Below is an example of an implementation of the
IsTraversableLiketrait where theReprtype isString.2.10