=:=
An instance ofA =:= B witnesses that the typesA andB are 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 (includingapply) 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 aFrom into aTo, andsubstituteContra replaces theTos in a type withFroms.
Type parameters
- From
a type which is proved equal to
To- To
a type which is proved equal to
From
Attributes
- See also
<:< for expressing subtyping constraints
- Example
An in-place variant ofscala.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.}- Source
- typeConstraints.scala
- Graph
- Supertypes
Members list
Value members
Abstract methods
SubstituteTo forFrom andFrom forTo in the typeF[To, From], given thatF is a type constructor of two arguments.
SubstituteTo forFrom andFrom forTo in the typeF[To, From], given thatF is a type constructor of two arguments. Essentially swapsTo andFrom inftf's type.
Equivalent in power to each ofsubstituteCo andsubstituteContra.
This method is impossible to implement withoutthrowing or otherwise "cheating" unlessFrom = To, so it ensures that this really represents a type equality.
Attributes
- Returns
ftf, $sameDiff- Definition Classes
- Source
- typeConstraints.scala
Concrete methods
IfFrom = To andTo = C, thenFrom = C (equality is transitive)
Coerce aFrom into aTo.
Coerce aFrom into aTo. This is guaranteed to be the identity function.
This method is often called implicitly as an implicitA =:= B doubles as an implicit viewA => B.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
IfFrom = To andC = From, thenC = To (equality is transitive)
IfFrom = To thenTo = From (equality is symmetric)
Lift this evidence over any type constructorF.
Lift this evidence over any type constructorF.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
Lift this evidence over the type constructorF, but flipped.
Lift this evidence over the type constructorF, but flipped.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
Substitute theFrom in the typeF[From], whereF is any type constructor, forTo.
Substitute theFrom in the typeF[From], whereF is any type constructor, forTo.
Equivalent in power to each ofsubstituteBoth andsubstituteContra.
This method is impossible to implement withoutthrowing or otherwise "cheating" unlessFrom = To, so it ensures that this really represents a type equality.
Attributes
- Returns
ff, $sameDiff- Definition Classes
- Source
- typeConstraints.scala
Substitute theTo in the typeF[To], whereF is any type constructor, forFrom.
Substitute theTo in the typeF[To], whereF is any type constructor, forFrom.
Equivalent in power to each ofsubstituteBoth andsubstituteCo.
This method is impossible to implement withoutthrowing or otherwise "cheating" unlessFrom = To, so it ensures that this really represents a type equality.
Attributes
- Returns
ft, $sameDiff- Definition Classes
- Source
- typeConstraints.scala
Inherited methods
IfFrom <: To andTo <: C, thenFrom <: C (subtyping is transitive)
IfFrom <: To andTo <: C, thenFrom <: C (subtyping is transitive)
Attributes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
Composes two instances ofFunction1 in a newFunction1, with this function applied first.
Composes two instances ofFunction1 in a newFunction1, with this function applied first.
Type parameters
- A
the result type of function
g
Value parameters
- g
a function R => A
Attributes
- Returns
a new function
fsuch thatf(x) == g(apply(x))- Definition Classes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
IfFrom <: To andC <: From, thenC <: To (subtyping is transitive)
IfFrom <: To andC <: From, thenC <: To (subtyping is transitive)
Attributes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
Composes two instances ofFunction1 in a newFunction1, with this function applied last.
Composes two instances ofFunction1 in a newFunction1, with this function applied last.
Type parameters
- A
the type to which function
gcan be applied
Value parameters
- g
a function A => T1
Attributes
- Returns
a new function
fsuch thatf(x) == apply(g(x))- Definition Classes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
Returns a string representation of the object.
Returns a string representation of the object.
The default representation is platform dependent.
Attributes
- Returns
a string representation of the object.
- Definition Classes
- Inherited from:
- Function1
- Source
- Function1.scala