add experimental API's for broadcast

base/Base.jl

@@ -348,6 +348,9 @@ include("util.jl")
 
 include("asyncmap.jl")
 
+# experimental API's
+include("experimental.jl")
+
 # deprecated functions
 include("deprecated.jl")
 

base/experimental.jl

@@ -0,0 +1,33 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+"""
+    Experimental
+
+Types, methods, or macros defined in this module are experimental and subject
+to change and will not have deprecations. Caveat emptor.
+"""
+module Experimental
+
+struct Const{T,N} <: DenseArray{T,N}
+    a::Array{T,N}
+end
+
+Base.IndexStyle(::Type{<:Const}) = IndexLinear()
+Base.size(C::Const) = size(C.a)
+Base.axes(C::Const) = axes(C.a)
+@eval Base.getindex(A::Const, i1::Int) =
+    (Base.@_inline_meta; Core.const_arrayref($(Expr(:boundscheck)), A.a, i1))
+@eval Base.getindex(A::Const, i1::Int, i2::Int, I::Int...) =
+  (Base.@_inline_meta; Core.const_arrayref($(Expr(:boundscheck)), A.a, i1, i2, I...))
+
+macro aliasscope(body)
+    sym = gensym()
+    esc(quote
+        $(Expr(:aliasscope))
+        $sym = $body
+        $(Expr(:popaliasscope))
+        $sym
+    end)
+end
+
+end