Use Val(x) and f(::Val{x})

Replaces `f(Val{x})` on call sites with `f(Val(x))`, using a new
`@pure` function `Val(x) = Val{x}()`. This simplifies the method
definitions from `f(::Type{Val{x}}) where x` to `f(::Val{x}) where x`.

This form also has the advantage that multiple singleton instances
can be put in a tuple and inference will work (similarly with
multiple-return functions).

NEWS.md

@@ -86,6 +86,12 @@ Library improvements
   * `@test isequal(x, y)` and `@test isapprox(x, y)` now prints an evaluated expression when
     the test fails ([#22296]).
 
+  * Uses of `Val{c}` in `Base` has been replaced with `Val{c}()`, which is now easily
+    accessible via the `@pure` constructor `Val(c)`. Functions are defined as
+    `f(::Val{c}) = ...` and called by `f(Val(c))`. Notable affected functions include:
+    `ntuple`, `Base.literal_pow`, `sqrtm`, `lufact`, `lufact!`, `qrfact`, `qrfact!`,
+    `cholfact`, `cholfact!`, `_broadcast!`, `reshape`, `cat` and `cat_t`.
+
 Compiler/Runtime improvements
 -----------------------------
 

base/abstractarray.jl

@@ -28,7 +28,7 @@ julia> size(A,3,2)
 """
 size(t::AbstractArray{T,N}, d) where {T,N} = d <= N ? size(t)[d] : 1
 size(x, d1::Integer, d2::Integer, dx::Vararg{Integer, N}) where {N} =
-    (size(x, d1), size(x, d2), ntuple(k->size(x, dx[k]), Val{N})...)
+    (size(x, d1), size(x, d2), ntuple(k->size(x, dx[k]), Val(N))...)
 
 """
     indices(A, d)
@@ -954,13 +954,13 @@ function _getindex(::IndexCartesian, A::AbstractArray{T,N}, I::Vararg{Int, N}) w
     getindex(A, I...)
 end
 _to_subscript_indices(A::AbstractArray, i::Int) = (@_inline_meta; _unsafe_ind2sub(A, i))
-_to_subscript_indices(A::AbstractArray{T,N}) where {T,N} = (@_inline_meta; fill_to_length((), 1, Val{N})) # TODO: DEPRECATE FOR #14770
+_to_subscript_indices(A::AbstractArray{T,N}) where {T,N} = (@_inline_meta; fill_to_length((), 1, Val(N))) # TODO: DEPRECATE FOR #14770
 _to_subscript_indices(A::AbstractArray{T,0}) where {T} = () # TODO: REMOVE FOR #14770
 _to_subscript_indices(A::AbstractArray{T,0}, i::Int) where {T} = () # TODO: REMOVE FOR #14770
 _to_subscript_indices(A::AbstractArray{T,0}, I::Int...) where {T} = () # TODO: DEPRECATE FOR #14770
 function _to_subscript_indices(A::AbstractArray{T,N}, I::Int...) where {T,N} # TODO: DEPRECATE FOR #14770
     @_inline_meta
-    J, Jrem = IteratorsMD.split(I, Val{N})
+    J, Jrem = IteratorsMD.split(I, Val(N))
     _to_subscript_indices(A, J, Jrem)
 end
 _to_subscript_indices(A::AbstractArray, J::Tuple, Jrem::Tuple{}) =
@@ -1203,7 +1203,7 @@ cat_shape(dims, shape::Tuple) = shape
 
 _cshp(ndim::Int, ::Tuple{}, ::Tuple{}, ::Tuple{}) = ()
 _cshp(ndim::Int, ::Tuple{}, ::Tuple{}, nshape) = nshape
-_cshp(ndim::Int, dims, ::Tuple{}, ::Tuple{}) = ntuple(b -> 1, Val{length(dims)})
+_cshp(ndim::Int, dims, ::Tuple{}, ::Tuple{}) = ntuple(b -> 1, Val(length(dims)))
 @inline _cshp(ndim::Int, dims, shape, ::Tuple{}) =
     (shape[1] + dims[1], _cshp(ndim + 1, tail(dims), tail(shape), ())...)
 @inline _cshp(ndim::Int, dims, ::Tuple{}, nshape) =
@@ -1226,7 +1226,7 @@ end
 _cs(d, a, b) = (a == b ? a : throw(DimensionMismatch(
     "mismatch in dimension $d (expected $a got $b)")))
 
-dims2cat(::Type{Val{n}}) where {n} = ntuple(i -> (i == n), Val{n})
+dims2cat(::Val{n}) where {n} = ntuple(i -> (i == n), Val(n))
 dims2cat(dims) = ntuple(i -> (i in dims), maximum(dims))
 
 cat(dims, X...) = cat_t(dims, promote_eltypeof(X...), X...)
@@ -1290,7 +1290,7 @@ julia> vcat(c...)
  4  5  6
 ```
 """
-vcat(X...) = cat(Val{1}, X...)
+vcat(X...) = cat(Val(1), X...)
 """
     hcat(A...)
 
@@ -1331,28 +1331,28 @@ julia> hcat(c...)
  3  6
 ```
 """
-hcat(X...) = cat(Val{2}, X...)
+hcat(X...) = cat(Val(2), X...)
 
-typed_vcat(T::Type, X...) = cat_t(Val{1}, T, X...)
-typed_hcat(T::Type, X...) = cat_t(Val{2}, T, X...)
+typed_vcat(T::Type, X...) = cat_t(Val(1), T, X...)
+typed_hcat(T::Type, X...) = cat_t(Val(2), T, X...)
 
 cat(catdims, A::AbstractArray{T}...) where {T} = cat_t(catdims, T, A...)
 
 # The specializations for 1 and 2 inputs are important
 # especially when running with --inline=no, see #11158
-vcat(A::AbstractArray) = cat(Val{1}, A)
-vcat(A::AbstractArray, B::AbstractArray) = cat(Val{1}, A, B)
-vcat(A::AbstractArray...) = cat(Val{1}, A...)
-hcat(A::AbstractArray) = cat(Val{2}, A)
-hcat(A::AbstractArray, B::AbstractArray) = cat(Val{2}, A, B)
-hcat(A::AbstractArray...) = cat(Val{2}, A...)
-
-typed_vcat(T::Type, A::AbstractArray) = cat_t(Val{1}, T, A)
-typed_vcat(T::Type, A::AbstractArray, B::AbstractArray) = cat_t(Val{1}, T, A, B)
-typed_vcat(T::Type, A::AbstractArray...) = cat_t(Val{1}, T, A...)
-typed_hcat(T::Type, A::AbstractArray) = cat_t(Val{2}, T, A)
-typed_hcat(T::Type, A::AbstractArray, B::AbstractArray) = cat_t(Val{2}, T, A, B)
-typed_hcat(T::Type, A::AbstractArray...) = cat_t(Val{2}, T, A...)
+vcat(A::AbstractArray) = cat(Val(1), A)
+vcat(A::AbstractArray, B::AbstractArray) = cat(Val(1), A, B)
+vcat(A::AbstractArray...) = cat(Val(1), A...)
+hcat(A::AbstractArray) = cat(Val(2), A)
+hcat(A::AbstractArray, B::AbstractArray) = cat(Val(2), A, B)
+hcat(A::AbstractArray...) = cat(Val(2), A...)
+
+typed_vcat(T::Type, A::AbstractArray) = cat_t(Val(1), T, A)
+typed_vcat(T::Type, A::AbstractArray, B::AbstractArray) = cat_t(Val(1), T, A, B)
+typed_vcat(T::Type, A::AbstractArray...) = cat_t(Val(1), T, A...)
+typed_hcat(T::Type, A::AbstractArray) = cat_t(Val(2), T, A)
+typed_hcat(T::Type, A::AbstractArray, B::AbstractArray) = cat_t(Val(2), T, A, B)
+typed_hcat(T::Type, A::AbstractArray...) = cat_t(Val(2), T, A...)
 
 # 2d horizontal and vertical concatenation
 
@@ -1721,7 +1721,7 @@ _sub2ind_vec(i) = ()
 
 function ind2sub(inds::Union{DimsInteger{N},Indices{N}}, ind::AbstractVector{<:Integer}) where N
     M = length(ind)
-    t = ntuple(n->similar(ind),Val{N})
+    t = ntuple(n->similar(ind),Val(N))
     for (i,idx) in enumerate(IndexLinear(), ind)
         sub = ind2sub(inds, idx)
         for j = 1:N

base/abstractarraymath.jl

@@ -368,8 +368,8 @@ julia> repeat([1 2; 3 4], inner=(2, 1), outer=(1, 3))
 ```
 """
 function repeat(A::AbstractArray;
-                inner=ntuple(n->1, Val{ndims(A)}),
-                outer=ntuple(n->1, Val{ndims(A)}))
+                inner=ntuple(n->1, Val(ndims(A))),
+                outer=ntuple(n->1, Val(ndims(A))))
     return _repeat(A, rep_kw2tup(inner), rep_kw2tup(outer))
 end
 

base/array.jl

@@ -85,7 +85,7 @@ end
 size(a::Array, d) = arraysize(a, d)
 size(a::Vector) = (arraysize(a,1),)
 size(a::Matrix) = (arraysize(a,1), arraysize(a,2))
-size(a::Array{<:Any,N}) where {N} = (@_inline_meta; ntuple(M -> size(a, M), Val{N}))
+size(a::Array{<:Any,N}) where {N} = (@_inline_meta; ntuple(M -> size(a, M), Val(N)))
 
 asize_from(a::Array, n) = n > ndims(a) ? () : (arraysize(a,n), asize_from(a, n+1)...)
 

base/bitarray.jl

@@ -480,7 +480,7 @@ reshape(B::BitArray, dims::Tuple{Vararg{Int}}) = _bitreshape(B, dims)
 function _bitreshape(B::BitArray, dims::NTuple{N,Int}) where N
     prod(dims) == length(B) ||
         throw(DimensionMismatch("new dimensions $(dims) must be consistent with array size $(length(B))"))
-    Br = BitArray{N}(ntuple(i->0,Val{N})...)
+    Br = BitArray{N}(ntuple(i->0,Val(N))...)
     Br.chunks = B.chunks
     Br.len = prod(dims)
     N != 1 && (Br.dims = dims)

base/broadcast.jl

@@ -134,7 +134,7 @@ Base.@propagate_inbounds _broadcast_getindex(::Any, A, I) = A[I]
 ## Broadcasting core
 # nargs encodes the number of As arguments (which matches the number
 # of keeps). The first two type parameters are to ensure specialization.
-@generated function _broadcast!(f, B::AbstractArray, keeps::K, Idefaults::ID, A::AT, Bs::BT, ::Type{Val{N}}, iter) where {K,ID,AT,BT,N}
+@generated function _broadcast!(f, B::AbstractArray, keeps::K, Idefaults::ID, A::AT, Bs::BT, ::Val{N}, iter) where {K,ID,AT,BT,N}
     nargs = N + 1
     quote
         $(Expr(:meta, :inline))
@@ -157,7 +157,7 @@ end
 
 # For BitArray outputs, we cache the result in a "small" Vector{Bool},
 # and then copy in chunks into the output
-@generated function _broadcast!(f, B::BitArray, keeps::K, Idefaults::ID, A::AT, Bs::BT, ::Type{Val{N}}, iter) where {K,ID,AT,BT,N}
+@generated function _broadcast!(f, B::BitArray, keeps::K, Idefaults::ID, A::AT, Bs::BT, ::Val{N}, iter) where {K,ID,AT,BT,N}
     nargs = N + 1
     quote
         $(Expr(:meta, :inline))
@@ -207,12 +207,12 @@ as in `broadcast!(f, A, A, B)` to perform `A[:] = broadcast(f, A, B)`.
     @boundscheck check_broadcast_indices(shape, A, Bs...)
     keeps, Idefaults = map_newindexer(shape, A, Bs)
     iter = CartesianRange(shape)
-    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val{N}, iter)
+    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val(N), iter)
     return C
 end
 
 # broadcast with computed element type
-@generated function _broadcast!(f, B::AbstractArray, keeps::K, Idefaults::ID, As::AT, ::Type{Val{nargs}}, iter, st, count) where {K,ID,AT,nargs}
+@generated function _broadcast!(f, B::AbstractArray, keeps::K, Idefaults::ID, As::AT, ::Val{nargs}, iter, st, count) where {K,ID,AT,nargs}
     quote
         $(Expr(:meta, :noinline))
         # destructure the keeps and As tuples
@@ -238,7 +238,7 @@ end
                     new[II] = B[II]
                 end
                 new[I] = V
-                return _broadcast!(f, new, keeps, Idefaults, As, Val{nargs}, iter, st, count+1)
+                return _broadcast!(f, new, keeps, Idefaults, As, Val(nargs), iter, st, count+1)
             end
             count += 1
         end
@@ -259,12 +259,12 @@ function broadcast_t(f, ::Type{Any}, shape, iter, As...)
         B = similar(Array{typeof(val)}, shape)
     end
     B[I] = val
-    return _broadcast!(f, B, keeps, Idefaults, As, Val{nargs}, iter, st, 1)
+    return _broadcast!(f, B, keeps, Idefaults, As, Val(nargs), iter, st, 1)
 end
 @inline function broadcast_t(f, T, shape, iter, A, Bs::Vararg{Any,N}) where N
     C = similar(Array{T}, shape)
     keeps, Idefaults = map_newindexer(shape, A, Bs)
-    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val{N}, iter)
+    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val(N), iter)
     return C
 end
 
@@ -275,7 +275,7 @@ end
 @inline function broadcast_t(f, ::Type{Bool}, shape, iter, A, Bs::Vararg{Any,N}) where N
     C = similar(BitArray, shape)
     keeps, Idefaults = map_newindexer(shape, A, Bs)
-    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val{N}, iter)
+    _broadcast!(f, C, keeps, Idefaults, A, Bs, Val(N), iter)
     return C
 end
 
@@ -335,9 +335,9 @@ end
 @inline broadcast_c(f, ::Type{Tuple}, A, Bs...) =
     tuplebroadcast(f, first_tuple(A, Bs...), A, Bs...)
 @inline tuplebroadcast(f, ::NTuple{N,Any}, As...) where {N} =
-    ntuple(k -> f(tuplebroadcast_getargs(As, k)...), Val{N})
+    ntuple(k -> f(tuplebroadcast_getargs(As, k)...), Val(N))
 @inline tuplebroadcast(f, ::NTuple{N,Any}, ::Type{T}, As...) where {N,T} =
-    ntuple(k -> f(T, tuplebroadcast_getargs(As, k)...), Val{N})
+    ntuple(k -> f(T, tuplebroadcast_getargs(As, k)...), Val(N))
 first_tuple(A::Tuple, Bs...) = A
 @inline first_tuple(A, Bs...) = first_tuple(Bs...)
 tuplebroadcast_getargs(::Tuple{}, k) = ()

base/deprecated.jl

@@ -1354,12 +1354,12 @@ end
 @deprecate versioninfo(io::IO, verbose::Bool) versioninfo(io, verbose=verbose)
 
 # PR #22188
-@deprecate cholfact!(A::StridedMatrix, uplo::Symbol, ::Type{Val{false}}) cholfact!(Hermitian(A, uplo), Val{false})
+@deprecate cholfact!(A::StridedMatrix, uplo::Symbol, ::Type{Val{false}}) cholfact!(Hermitian(A, uplo), Val(false))
 @deprecate cholfact!(A::StridedMatrix, uplo::Symbol) cholfact!(Hermitian(A, uplo))
-@deprecate cholfact(A::StridedMatrix, uplo::Symbol, ::Type{Val{false}}) cholfact(Hermitian(A, uplo), Val{false})
+@deprecate cholfact(A::StridedMatrix, uplo::Symbol, ::Type{Val{false}}) cholfact(Hermitian(A, uplo), Val(false))
 @deprecate cholfact(A::StridedMatrix, uplo::Symbol) cholfact(Hermitian(A, uplo))
-@deprecate cholfact!(A::StridedMatrix, uplo::Symbol, ::Type{Val{true}}; tol = 0.0) cholfact!(Hermitian(A, uplo), Val{true}, tol = tol)
-@deprecate cholfact(A::StridedMatrix, uplo::Symbol, ::Type{Val{true}}; tol = 0.0) cholfact(Hermitian(A, uplo), Val{true}, tol = tol)
+@deprecate cholfact!(A::StridedMatrix, uplo::Symbol, ::Type{Val{true}}; tol = 0.0) cholfact!(Hermitian(A, uplo), Val(true), tol = tol)
+@deprecate cholfact(A::StridedMatrix, uplo::Symbol, ::Type{Val{true}}; tol = 0.0) cholfact(Hermitian(A, uplo), Val(true), tol = tol)
 
 # PR #22245
 @deprecate isposdef(A::AbstractMatrix, UL::Symbol) isposdef(Hermitian(A, UL))
@@ -1519,6 +1519,30 @@ function replace(s::AbstractString, pat, f, n::Integer)
     end
 end
 
+# PR #22475
+@deprecate ntuple{N}(f, ::Type{Val{N}}) ntuple(f, Val(N))
+@deprecate fill_to_length{N}(t, val, ::Type{Val{N}}) fill_to_length(t, val, Val(N)) false
+@deprecate literal_pow{N}(a, b, ::Type{Val{N}}) literal_pow(a, b, Val(N)) false
+@eval IteratorsMD @deprecate split{n}(t, V::Type{Val{n}}) split(t, Val(n)) false
+@deprecate sqrtm{T,realmatrix}(A::UpperTriangular{T},::Type{Val{realmatrix}}) sqrtm(A, Val(realmatrix))
+@deprecate lufact(A::AbstractMatrix, ::Type{Val{false}}) lufact(A, Val(false))
+@deprecate lufact(A::AbstractMatrix, ::Type{Val{true}}) lufact(A, Val(true))
+@deprecate lufact!(A::AbstractMatrix, ::Type{Val{false}}) lufact!(A, Val(false))
+@deprecate lufact!(A::AbstractMatrix, ::Type{Val{true}}) lufact!(A, Val(true))
+@deprecate qrfact(A::AbstractMatrix, ::Type{Val{false}}) qrfact(A, Val(false))
+@deprecate qrfact(A::AbstractMatrix, ::Type{Val{true}}) qrfact(A, Val(true))
+@deprecate qrfact!(A::AbstractMatrix, ::Type{Val{false}}) qrfact!(A, Val(false))
+@deprecate qrfact!(A::AbstractMatrix, ::Type{Val{true}}) qrfact!(A, Val(true))
+@deprecate cholfact(A::AbstractMatrix, ::Type{Val{false}}) cholfact(A, Val(false))
+@deprecate cholfact(A::AbstractMatrix, ::Type{Val{true}}; tol = 0.0) cholfact(A, Val(true); tol = tol)
+@deprecate cholfact!(A::AbstractMatrix, ::Type{Val{false}}) cholfact!(A, Val(false))
+@deprecate cholfact!(A::AbstractMatrix, ::Type{Val{true}}; tol = 0.0) cholfact!(A, Val(true); tol = tol)
+@deprecate cat{N}(::Type{Val{N}}, A::AbstractArray...) cat(Val(N), A...)
+@deprecate cat{N}(::Type{Val{N}}, A::SparseArrays._SparseConcatGroup...) cat(Val(N), A...)
+@deprecate cat{N}(::Type{Val{N}}, A::SparseArrays._DenseConcatGroup...) cat(Val(N), A...)
+@deprecate cat_t{N,T}(::Type{Val{N}}, ::Type{T}, A, B) cat_t(Val(N), T, A, B) false
+@deprecate reshape{N}(A::AbstractArray, ::Type{Val{N}}) reshape(A, Val(N))
+
 # END 0.7 deprecations
 
 # BEGIN 1.0 deprecations

base/essentials.jl

@@ -313,18 +313,33 @@ struct Colon
 end
 const (:) = Colon()
 
-# For passing constants through type inference
 """
-    Val{c}
+    Val(c)
 
-Create a "value type" out of `c`, which must be an `isbits` value. The intent of this
-construct is to be able to dispatch on constants, e.g., `f(Val{false})` allows you to
-dispatch directly (at compile-time) to an implementation `f(::Type{Val{false}})`, without
-having to test the boolean value at runtime.
+Return `Val{c}()`, which contains no run-time data. Types like this can be used to
+pass the information between functions through the value `c`, which must be an `isbits`
+value. The intent of this construct is to be able to dispatch on constants directly (at
+compile time) without having to test the value of the constant at run time.
+
+# Examples
+```jldoctest
+julia> f(::Val{true}) = "Good"
+f (generic function with 1 method)
+
+julia> f(::Val{false}) = "Bad"
+f (generic function with 2 methods)
+
+julia> f(Val(true))
+"Good"
+```
 """
-struct Val{T}
+struct Val{x}
 end
 
+Val(x) = (@_pure_meta; Val{x}())
+
+show(io::IO, ::Val{x}) where {x} = print(io, "Val($x)")
+
 # used by interpolating quote and some other things in the front end
 function vector_any(xs::ANY...)
     n = length(xs)

base/intfuncs.jl

@@ -198,14 +198,14 @@ end
 ^(x::Number, p::Integer)  = power_by_squaring(x,p)
 ^(x, p::Integer)          = power_by_squaring(x,p)
 
-# x^p for any literal integer p is lowered to Base.literal_pow(^, x, Val{p})
+# x^p for any literal integer p is lowered to Base.literal_pow(^, x, Val(p))
 # to enable compile-time optimizations specialized to p.
 # However, we still need a fallback that calls the function ^ which may either
 # mean Base.^ or something else, depending on context.
 # We mark these @inline since if the target is marked @inline,
 # we want to make sure that gets propagated,
 # even if it is over the inlining threshold.
-@inline literal_pow(f, x, ::Type{Val{p}}) where {p} = f(x,p)
+@inline literal_pow(f, x, ::Val{p}) where {p} = f(x,p)
 
 # Restrict inlining to hardware-supported arithmetic types, which
 # are fast enough to benefit from inlining.
@@ -216,10 +216,10 @@ const HWNumber = Union{HWReal, Complex{<:HWReal}, Rational{<:HWReal}}
 # numeric types.  In terms of Val we can do it much more simply.
 # (The first argument prevents unexpected behavior if a function ^
 # is defined that is not equal to Base.^)
-@inline literal_pow(::typeof(^), x::HWNumber, ::Type{Val{0}}) = one(x)
-@inline literal_pow(::typeof(^), x::HWNumber, ::Type{Val{1}}) = x
-@inline literal_pow(::typeof(^), x::HWNumber, ::Type{Val{2}}) = x*x
-@inline literal_pow(::typeof(^), x::HWNumber, ::Type{Val{3}}) = x*x*x
+@inline literal_pow(::typeof(^), x::HWNumber, ::Val{0}) = one(x)
+@inline literal_pow(::typeof(^), x::HWNumber, ::Val{1}) = x
+@inline literal_pow(::typeof(^), x::HWNumber, ::Val{2}) = x*x
+@inline literal_pow(::typeof(^), x::HWNumber, ::Val{3}) = x*x*x
 
 # b^p mod m
 

base/linalg/arnoldi.jl

@@ -339,7 +339,7 @@ function A_mul_B!(y::StridedVector{T}, A::AtA_or_AAt{T}, x::StridedVector{T}) wh
         return A_mul_B!(y, A.A, A.buffer)
     end
 end
-size(A::AtA_or_AAt) = ntuple(i -> min(size(A.A)...), Val{2})
+size(A::AtA_or_AAt) = ntuple(i -> min(size(A.A)...), Val(2))
 ishermitian(s::AtA_or_AAt) = true