Class scala.=:=
sealed abstract class =:=[From, To] extends <:<[From, To] with Serializable
Abstract Value Members
abstract def substituteBoth[F[_, _]](ftf: F[To, From]): F[From, To]
Substitute To for From and From for To in the type F[To, From], given that F is a type constructor of two arguments. Essentially swaps To and From in ftf's type.
Equivalent in power to each of substituteCo and substituteContra.
This method is impossible to implement without throwing or otherwise "cheating" unless From = To, so it ensures that this really represents a type equality.
- returns
ftf, but with a (potentially) different type
Concrete Value Members
final def !=(arg0: Any): Boolean
Test two objects for inequality.
- returns
trueif !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
final def ##(): Int
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.
- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
def +(other: String): String
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toany2stringadd[=:=[From, To]] performed by method any2stringadd in scala.Predef.
- Definition Classes
- any2stringadd
def ->[B](y: B): (=:=[From, To], B)
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toArrowAssoc[=:=[From, To]] performed by method ArrowAssoc in scala.Predef.This conversion will take place only if To is a subclass of Option[Nothing] (To <: Option[Nothing]).
- Definition Classes
- ArrowAssoc
- Annotations
- @inline()
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
def andThen[C](r: =:=[To, C]): =:=[From, C]
def andThen[C](r: <:<[To, C]): <:<[From, C]
If From <: To and To <: C, then From <: C (subtyping is transitive)
- Definition Classes
- <:<
def andThen[C](r: (To) => C): (From) => C
Composes two instances of Function1 in a new Function1, with this function applied first.
- returns
a new function
fsuch thatf(x) == g(apply(x))
def apply(f: From): To
Coerce a From into a To. This is guaranteed to be the identity function.
This method is often called implicitly as an implicit A =:= B doubles as an implicit view A => B.
- f
some value of type
From- returns
f, but with a (potentially) different type
final def asInstanceOf[T0]: T0
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.
- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastExceptionif the receiver object is not an instance of the erasure of typeT0.
def clone(): AnyRef
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
- returns
a copy of the receiver object.
def compose[C](r: =:=[C, From]): =:=[C, To]
def compose[C](r: <:<[C, From]): <:<[C, To]
If From <: To and C <: From, then C <: To (subtyping is transitive)
- Definition Classes
- <:<
def compose[C](r: (C) => From): (C) => To
Composes two instances of Function1 in a new Function1, with this function applied last.
- returns
a new function
fsuch thatf(x) == apply(g(x))
def ensuring(cond: (=:=[From, To]) => Boolean, msg: => Any): =:=[From, To]
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toEnsuring[=:=[From, To]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: (=:=[From, To]) => Boolean): =:=[From, To]
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toEnsuring[=:=[From, To]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: Boolean, msg: => Any): =:=[From, To]
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toEnsuring[=:=[From, To]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
def ensuring(cond: Boolean): =:=[From, To]
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toEnsuring[=:=[From, To]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
final def eq(arg0: AnyRef): Boolean
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:
-
It is consistent: for any non-null instances
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).
- returns
trueif the argument is a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
def equals(arg0: AnyRef): Boolean
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
def finalize(): Unit
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.
def flip: =:=[To, From]
def formatted(fmtstr: String): String
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toStringFormat[=:=[From, To]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @inline()
final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- returns
a class object corresponding to the runtime type of the receiver.
def hashCode(): Int
The hashCode method for reference types. See hashCode in scala.Any.
- returns
the hash code value for this object.
final def isInstanceOf[T0]: Boolean
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.
- returns
trueif the receiver object is an instance of erasure of typeT0;falseotherwise.
- Definition Classes
- Any
def liftCo[F[_]]: =:=[F[From], F[To]]
def liftContra[F[_]]: =:=[F[To], F[From]]
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
- returns
trueif the argument is not a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
- Definition Classes
- AnyRef
- Annotations
- @native()
- Note
not specified by SLS as a member of AnyRef
def substituteCo[F[_]](ff: F[From]): F[To]
Substitute the From in the type F[From], where F is any type constructor, for To.
Equivalent in power to each of substituteBoth and substituteContra.
This method is impossible to implement without throwing or otherwise "cheating" unless From = To, so it ensures that this really represents a type equality.
- returns
ff, but with a (potentially) different type
def substituteContra[F[_]](ft: F[To]): F[From]
Substitute the To in the type F[To], where F is any type constructor, for From.
Equivalent in power to each of substituteBoth and substituteCo.
This method is impossible to implement without throwing or otherwise "cheating" unless From = To, so it ensures that this really represents a type equality.
- returns
ft, but with a (potentially) different type
final def synchronized[T0](arg0: => T0): T0
- Definition Classes
- AnyRef
def toString(): 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.
- returns
a String representation of the object.
def unlift: PartialFunction[From, B]
Converts an optional function to a partial function.
- Implicit
- This member is added by an implicit conversion from =:=[From, To] toUnliftOps[From, B] performed by method UnliftOps in scala.Function1.This conversion will take place only if To is a subclass of Option[B] (To <: Option[B]).
- Definition Classes
- UnliftOps
Unlike Function.unlift, this UnliftOps.unlift method can be used in extractors.
val of: Int => Option[String] = { i =>
if (i == 2) {
Some("matched by an optional function")
} else {
None
}
}
util.Random.nextInt(4) match {
case of.unlift(m) => // Convert an optional function to a pattern
println(m)
case _ =>
println("Not matched")
}
final def wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long): Unit
© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/$eq$colon$eq.html
An instance of
A =:= Bwitnesses that the typesAandBare equal. It also acts as aA <:< B, but not aB <:< A(directly) due to restrictions on subclassing.In case of any confusion over which method goes in what direction, all the "Co" methods (including apply) go from left to right in the type ("with" the type), and all the "Contra" methods go from right to left ("against" the type). E.g., apply turns a
Frominto aTo, and substituteContra replaces theTos in a type withFroms.a type which is proved equal to
Toa type which is proved equal to
FromAn in-place variant of scala.collection.mutable.ArrayBuffer#transpose
implicit class BufOps[A](private val buf: ArrayBuffer[A]) extends AnyVal { def inPlaceTranspose[E]()(implicit ev: A =:= ArrayBuffer[E]) = ??? // Because ArrayBuffer is invariant, we can't make do with just a A <:< ArrayBuffer[E] // Getting buffers *out* from buf would work, but adding them back *in* wouldn't. }<:< for expressing subtyping constraints