add isdisjoint (JuliaLang/julia#34427) (#695)

* add isdisjoint (JuliaLang/julia#34427)

* fix formatting

* Use correct version in README entry

* Add missing link to README

And sort/unify the entries using NEWS-update.jl

Co-authored-by: colinxs <me@colinxsummers.com>
Co-authored-by: Martin Holters <martin.holters@hsu-hh.de>

README.md

@@ -44,6 +44,8 @@ Please check the list below for the specific syntax you need.
 
 ## Supported features
 
+* `isdisjoint(l, r)` indicates whether two collections are disjoint ([#34427]). (since Compat 3.9.0)
+
 * `mergewith(combine, dicts...)` and `mergewith!(combine, dicts...)` are like
   `merge(combine, dicts...)` and `merge!(combine, dicts...)` but without the restriction
   that the argument `combine` must be a `Function` ([#34296]). (since Compat 3.9.0).
@@ -138,7 +140,8 @@ Note that you should specify the correct minimum version for `Compat` in the
 [#33129]: https://github.com/JuliaLang/julia/issues/33129
 [#33568]: https://github.com/JuliaLang/julia/issues/33568
 [#33736]: https://github.com/JuliaLang/julia/issues/33736
-[#34548]: https://github.com/JuliaLang/julia/pull/34548
+[#34296]: https://github.com/JuliaLang/julia/issues/34296
+[#34427]: https://github.com/JuliaLang/julia/issues/34427
+[#34548]: https://github.com/JuliaLang/julia/issues/34548
 [#34652]: https://github.com/JuliaLang/julia/issues/34652
 [#34773]: https://github.com/JuliaLang/julia/issues/34773
-[#34296]: https://github.com/JuliaLang/julia/pull/34296

src/Compat.jl

@@ -356,6 +356,36 @@ if VERSION < v"1.5.0-DEV.182"
     mergewith!(f) = (dicts...) -> mergewith!(f, dicts...)
 end
 
+# https://github.com/JuliaLang/julia/pull/32003
+if VERSION < v"1.4.0-DEV.29"
+    hasfastin(::Type) = false
+    hasfastin(::Union{Type{<:AbstractSet},Type{<:AbstractDict},Type{<:AbstractRange}}) = true
+    hasfastin(x) = hasfastin(typeof(x))
+else
+    const hasfastin = Base.hasfastin
+end
+
+# https://github.com/JuliaLang/julia/pull/34427
+if VERSION < v"1.5.0-DEV.124"
+    const FASTIN_SET_THRESHOLD = 70
+
+    function isdisjoint(l, r)
+        function _isdisjoint(l, r)
+            hasfastin(r) && return !any(in(r), l)
+            hasfastin(l) && return !any(in(l), r)
+            Base.haslength(r) && length(r) < FASTIN_SET_THRESHOLD &&
+                return !any(in(r), l)
+            return !any(in(Set(r)), l)
+        end
+        if Base.haslength(l) && Base.haslength(r) && length(r) < length(l)
+            return _isdisjoint(r, l)
+        end
+        _isdisjoint(l, r)
+    end
+
+    export isdisjoint
+end
+
 include("deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -337,4 +337,25 @@ end
         Dict("A" => 1, "B" => 21, "C" => 36)
 end
 
+# https://github.com/JuliaLang/julia/pull/34427
+@testset "isdisjoint" begin
+    for S in (Set, BitSet, Vector)
+        for (l,r) in ((S([1,2]),     S([3,4])),
+                      (S([5,6,7,8]), S([7,8,9])),
+                      (S([1,2]),     S([3,4])),
+                      (S([5,6,7,8]), S([7,8,9])),
+                      (S([1,2,3]),   S()),
+                      (S(),          S()),
+                      (S(),          S([1,2,3])),
+                      (S([1,2,3]),   S([1])),
+                      (S([1,2,3]),   S([1,2])),
+                      (S([1,2,3]),   S([1,2,3])),
+                      (S([1,2,3]),   S([4])),
+                      (S([1,2,3]),   S([4,1])))
+            @test isdisjoint(l,l) == isempty(l)
+            @test isdisjoint(l,r) == isempty(intersect(l,r))
+        end
+    end
+end
+
 nothing