Add @functorize

README.md

@@ -160,6 +160,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `@inline` and `@noinline` have been added. On 0.3, these are "no-ops," meaning they don't actually do anything.
 
+* `@functorize` (not present in any Julia version) takes a function (or operator) and turns it into a functor object if one is available in the used Julia version. E.g. something like `mapreduce(Base.AbsFun(), Base.MulFun(), x)` can now be written as `mapreduce(@functorize(abs), @functorize(*), x)` to work accross different Julia versions.
+
 ## Other changes
 
 * `Dict(ks, vs)` is now `Dict(zip(ks, vs))` [#8521](https://github.com/JuliaLang/julia/pull/8521)

src/Compat.jl

@@ -980,4 +980,81 @@ if !isdefined(Base, :istextmime)
     istextmime(m::@compat(Union{MIME,AbstractString})) = istext(m)
 end
 
+export @functorize
+macro functorize(f)
+    if VERSION >= v"0.5.0-dev+3701"
+        f === :scalarmax       ? :(Base.scalarmax) :
+        f === :scalarmin       ? :(Base.scalarmin) :
+        f === :centralizedabs2fun ? :(typeof(Base.centralizedabs2fun(0)).name.primary) :
+        f
+    else
+        f = f === :identity        ? :(Base.IdFun()) :
+            f === :abs             ? :(Base.AbsFun()) :
+            f === :abs2            ? :(Base.Abs2Fun()) :
+            f === :exp             ? :(Base.ExpFun()) :
+            f === :log             ? :(Base.LogFun()) :
+            f === :&               ? :(Base.AndFun()) :
+            f === :|               ? :(Base.OrFun()) :
+            f === :+               ? :(Base.AddFun()) :
+            f === :*               ? :(Base.MulFun()) :
+            f === :scalarmax       ? :(Base.MaxFun()) :
+            f === :scalarmin       ? :(Base.MinFun()) :
+            f === :centralizedabs2fun ? :(Base.CentralizedAbs2Fun) :
+            f
+        if VERSION >= v"0.4.0-dev+4902"
+            f = f === :<           ? :(Base.LessFun()) :
+                f === :>           ? :(Base.MoreFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-dev+4902"
+            f = f === :conj        ? :(Base.ConjFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-dev+6254"
+            f = f === :-           ? :(Base.SubFun()) :
+                f === :^           ? :(Base.PowFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-dev+6256"
+            f = f === :/           ? :(Base.RDivFun()) :
+                f === :\           ? :(Base.LDivFun()) :
+                f === :div         ? :(Base.IDivFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-dev+6353"
+            f = f === :$           ? :(Base.XorFun()) :
+                f === :.+          ? :(Base.DotAddFun()) :
+                f === :.-          ? :(Base.DotSubFun()) :
+                f === :.*          ? :(Base.DotMulFun()) :
+                f === :mod         ? :(Base.ModFun()) :
+                f === :rem         ? :(Base.RemFun()) :
+                # DotRemFun is defined, but ::call(::DotRemFun, ...) is not until later
+                #f === :.%          ? :(Base.DotRemFun()) :
+                f === :.<<         ? :(Base.DotLSFun()) :
+                f === :.>>         ? :(Base.DotRSFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-dev+6359"
+            f = f === :./          ? :(Base.DotRDivFun()) :
+                f
+        end
+        if VERSION >= v"0.4.0-rc1+59"
+            f = f === :max         ? :(Base.ElementwiseMaxFun()) :
+                f === :min         ? :(Base.ElementwiseMinFun()) :
+                f
+        end
+        if VERSION >= v"0.5.0-dev+741"
+            f = f === :complex     ? :(Base.SparseArrays.ComplexFun()) :
+                f === :dot         ? :(Base.SparseArrays.DotFun()) :
+                f
+        end
+        if VERSION >= v"0.5.0-dev+1472"
+            f = f === symbol(".÷") ? :(Base.DotIDivFun()) :
+                f === :.%          ? :(Base.DotRemFun()) :
+                f
+        end
+        f
+    end
+end
+
 end # module

test/runtests.jl

@@ -1004,3 +1004,90 @@ if VERSION < v"0.4.0"
 else
     @compat rc = RemoteChannel{Channel{Any}}(1,2,3)
 end
+
+# @functorize
+function checkfunc(Fun, func)
+    if VERSION >= v"0.5.0-dev+3701"
+        @eval @test @functorize($(func)) === Base.$(func)
+    else
+        if isdefined(Base, Fun)
+            @eval @test isa(@functorize($(func)), Base.$(Fun))
+        else
+            @eval @test isa(@functorize($(func)), Function)
+            @eval @test @functorize($(func)) === Base.$(func)
+        end
+    end
+end
+
+for (Fun, func) in [(:IdFun,                   :identity),
+                    (:AbsFun,                  :abs),
+                    (:Abs2Fun,                 :abs2),
+                    (:ExpFun,                  :exp),
+                    (:LogFun,                  :log),
+                    (:ConjFun,                 :conj)]
+    begin
+        if isdefined(Base, func)
+            checkfunc(Fun, func)
+            a = rand(1:10, 10)
+            @eval @test mapreduce($(func), +, $(a)) == mapreduce(@functorize($(func)), +, $(a))
+        end
+    end
+end
+
+for (Fun, func) in [(:AndFun,              :&),
+                    (:OrFun,               :|),
+                    (:XorFun,              :$),
+                    (:AddFun,              :+),
+                    (:DotAddFun,           :.+),
+                    (:SubFun,              :-),
+                    (:DotSubFun,           :.-),
+                    (:MulFun,              :*),
+                    (:DotMulFun,           :.*),
+                    (:RDivFun,             :/),
+                    (:DotRDivFun,          :./),
+                    (:LDivFun,             :\),
+                    (:IDivFun,             :div),
+                    (:DotIDivFun,          symbol(".÷")),
+                    (:ModFun,              :mod),
+                    (:RemFun,              :rem),
+                    (:DotRemFun,           :.%),
+                    (:PowFun,              :^),
+                    (:MaxFun,              :scalarmax),
+                    (:MinFun,              :scalarmin),
+                    (:LessFun,             :<),
+                    (:MoreFun,             :>),
+                    (:DotLSFun,            :.<<),
+                    (:DotRSFun,            :.>>),
+                    (:ElementwiseMaxFun,   :max),
+                    (:ElementwiseMinFun,   :min)]
+    begin
+        if isdefined(Base, func) && (func !== :.>> || VERSION >= v"0.4.0-dev+553") && (func !== :.% || VERSION >= v"0.5.0-dev+1472")
+            checkfunc(Fun, func)
+            a = rand(1:10, 10)
+            @eval @test mapreduce(identity, Base.$(func), $(a)) == mapreduce(identity, @functorize($(func)), $(a))
+        end
+    end
+end
+
+if VERSION >= v"0.5.0-dev+3701"
+    @test @functorize(complex) === complex
+    @test @functorize(dot) === dot
+else
+    if isdefined(Base, :SparseArrays) && isdefined(Base.SparseArrays, :ComplexFun)
+        @test isa(@functorize(complex), Base.SparseArrays.ComplexFun)
+        @test isa(@functorize(dot), Base.SparseArrays.DotFun)
+    else
+        @test isa(@functorize(complex), Function)
+        @test isa(@functorize(dot), Function)
+        @test @functorize(complex) === complex
+        @test @functorize(dot) === dot
+    end
+end
+let a = rand(1:10, 10)
+    @test mapreduce(identity, dot, a) == mapreduce(identity, @functorize(dot), a)
+end
+@test isa(@functorize(centralizedabs2fun)(1), @functorize(centralizedabs2fun))
+@test isa(@functorize(centralizedabs2fun)(1.0), @functorize(centralizedabs2fun))
+let a = rand(1:10, 10)
+    @eval @test mapreduce(x -> abs2(x - 1), +, $(a)) == mapreduce(@functorize(centralizedabs2fun)(1), +, $(a))
+end