=:=
An instance of A =:= B
witnesses that the types A
and B
are equal. It also acts as a A <:< B
, but not a B <:< 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 From
into a To
, and substituteContra replaces the To
s in a type with From
s.
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 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. }
- Source
- typeConstraints.scala
- Graph
-
- Supertypes
Members list
Value members
Abstract methods
Substitute To
for From
and From
for To
in the type F[To, From]
, given that F
is a type constructor of two arguments.
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 throw
ing or otherwise "cheating" unless From = To
, so it ensures that this really represents a type equality.
Attributes
- Returns
-
ftf
, $sameDiff - Definition Classes
- Source
- typeConstraints.scala
Concrete methods
If From = To
and To = C
, then From = C
(equality is transitive)
If From = To
and To = C
, then From = C
(equality is transitive)
Attributes
- Source
- typeConstraints.scala
Coerce a From
into a 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
.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
If From = To
and C = From
, then C = To
(equality is transitive)
If From = To
and C = From
, then C = To
(equality is transitive)
Attributes
- Source
- typeConstraints.scala
If From = To
then To = From
(equality is symmetric)
Lift this evidence over any type constructor F
.
Lift this evidence over any type constructor F
.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
Lift this evidence over the type constructor F
, but flipped.
Lift this evidence over the type constructor F
, but flipped.
Attributes
- Definition Classes
- Source
- typeConstraints.scala
Substitute the From
in the type F[From]
, where F
is any type constructor, for 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 throw
ing or otherwise "cheating" unless From = To
, so it ensures that this really represents a type equality.
Attributes
- Returns
-
ff
, $sameDiff - Definition Classes
- Source
- typeConstraints.scala
Substitute the To
in the type F[To]
, where F
is any type constructor, for 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 throw
ing or otherwise "cheating" unless From = To
, so it ensures that this really represents a type equality.
Attributes
- Returns
-
ft
, $sameDiff - Definition Classes
- Source
- typeConstraints.scala
Inherited methods
If From <: To
and To <: C
, then From <: C
(subtyping is transitive)
If From <: To
and To <: C
, then From <: C
(subtyping is transitive)
Attributes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
Composes two instances of Function1
in a new Function1
, with this function applied first.
Composes two instances of Function1
in a new Function1
, 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
f
such thatf(x) == g(apply(x))
- Definition Classes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
If From <: To
and C <: From
, then C <: To
(subtyping is transitive)
If From <: To
and C <: From
, then C <: To
(subtyping is transitive)
Attributes
- Inherited from:
- <:<
- Source
- typeConstraints.scala
Composes two instances of Function1
in a new Function1
, with this function applied last.
Composes two instances of Function1
in a new Function1
, with this function applied last.
Type parameters
- A
-
the type to which function
g
can be applied
Value parameters
- g
-
a function A => T1
Attributes
- Returns
-
a new function
f
such 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