We need a whole WithFilter class to honor the "doesn't create a new collection" contract even though it seems unlikely to matter much in a collection with max size 1.
A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.
the value being probed for possible equality
true if this instance can possibly equal that, otherwise false
Inverts this Try. If this is a Failure, returns its exception wrapped in a Success. If this is a Success, returns a Failure containing an UnsupportedOperationException.
Applies fa if this is a Failure or fb if this is a Success. If fb is initially applied and throws an exception, then fa is applied with this exception.
the function to apply if this is a Failure
the function to apply if this is a Success
the results of applying the function
val result: Try[Throwable, Int] = Try { string.toInt }
log(result.fold(
ex => "Operation failed with " + ex,
v => "Operation produced value: " + v
))
Applies the given function f if this is a Success, otherwise returns Unit if this is a Failure.
Note: If f throws, then this method may throw an exception.
Returns the value from this Success or the given default argument if this is a Failure.
Note:: This will throw an exception if it is not a success and default throws an exception.
The size of this product.
for a product A(x1, ..., xk), returns k
The nth element of this product, 0-based. In other words, for a product A(x1, ..., xk), returns x(n+1) where 0 <= n < k.
the index of the element to return
the element n elements after the first element
Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like map for the exception.
Applies the given function f if this is a Failure, otherwise returns this if this is a Success. This is like flatMap for the exception.
Test two objects for inequality.
true if !(this == that), false otherwise.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
a hash value consistent with ==
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
true if the receiver object is equivalent to the argument; false otherwise.
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
the receiver object.
ClassCastException if the receiver object is not an instance of the erasure of type T0.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
a copy of the receiver object.
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
null.eq(null) returns true. When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
true if the argument is a reference to the receiver object; false otherwise.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
true if the receiver object is equivalent to the argument; false otherwise.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.
not specified by SLS as a member of AnyRef
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
Returns the runtime class representation of the object.
a class object corresponding to the runtime type of the receiver.
The hashCode method for reference types. See hashCode in scala.Any.
the hash code value for this object.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
true if the receiver object is an instance of erasure of type T0; false otherwise.
Equivalent to !(this eq that).
true if the argument is not a reference to the receiver object; false otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
Wakes up all threads that are waiting on the receiver object's monitor.
not specified by SLS as a member of AnyRef
An iterator over all the elements of this product.
in the default implementation, an Iterator[Any]
A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.
in the default implementation, the empty string
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
a String representation of the object.
Creates a non-strict filter, which eventually converts this to a Failure if the predicate is not satisfied.
Note: unlike filter, withFilter does not create a new Try. Instead, it restricts the domain of subsequent map, flatMap, foreach, and withFilter operations.
As Try is a one-element collection, this may be a bit overkill, but it's consistent with withFilter on Option and the other collections.
the predicate used to test elements.
an object of class WithFilter, which supports map, flatMap, foreach, and withFilter operations. All these operations apply to those elements of this Try which satisfy the predicate p.
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/util/Try.html
The
Trytype represents a computation that may either result in an exception, or return a successfully computed value. It's similar to, but semantically different from the scala.util.Either type.Instances of
Try[T], are either an instance of scala.util.Success[T] or scala.util.Failure[T].For example,
Trycan be used to perform division on a user-defined input, without the need to do explicit exception-handling in all of the places that an exception might occur.Example:
import scala.io.StdIn import scala.util.{Try, Success, Failure} def divide: Try[Int] = { val dividend = Try(StdIn.readLine("Enter an Int that you'd like to divide:\n").toInt) val divisor = Try(StdIn.readLine("Enter an Int that you'd like to divide by:\n").toInt) val problem = dividend.flatMap(x => divisor.map(y => x/y)) problem match { case Success(v) => println("Result of " + dividend.get + "/"+ divisor.get +" is: " + v) Success(v) case Failure(e) => println("You must've divided by zero or entered something that's not an Int. Try again!") println("Info from the exception: " + e.getMessage) divide } }An important property of
Tryshown in the above example is its ability to pipeline, or chain, operations, catching exceptions along the way. TheflatMapandmapcombinators in the above example each essentially pass off either their successfully completed value, wrapped in theSuccesstype for it to be further operated upon by the next combinator in the chain, or the exception wrapped in theFailuretype usually to be simply passed on down the chain. Combinators such asrecoverandrecoverWithare designed to provide some type of default behavior in the case of failure.Note: only non-fatal exceptions are caught by the combinators on
Try(see scala.util.control.NonFatal). Serious system errors, on the other hand, will be thrown.Note:: all Try combinators will catch exceptions and return failure unless otherwise specified in the documentation.
Trycomes to the Scala standard library after years of use as an integral part of Twitter's stack.2.10