Allows the results of mapfoldr to be inferred on tuples. (#33235)

JuliaLang · Oct 3, 2019 · bf8c324 · bf8c324
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commit bf8c324
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diff --git a/base/iterators.jl b/base/iterators.jl
@@ -98,6 +98,7 @@ reverse(G::Generator) = Generator(G.f, reverse(G.iter))
 reverse(r::Reverse) = r.itr
 reverse(x::Union{Number,AbstractChar}) = x
 reverse(p::Pair) = Base.reverse(p) # copying pairs is cheap
+reverse(xs::Tuple) = Base.reverse(xs) # allows inference in mapfoldr and similar
 
 iterate(r::Reverse{<:Tuple}, i::Int = length(r.itr)) = i < 1 ? nothing : (r.itr[i], i-1)
 

diff --git a/test/reduce.jl b/test/reduce.jl
@@ -30,6 +30,8 @@ using .Main.OffsetArrays
 
 @test Base.mapfoldr(abs2, -, 2:5) == -14
 @test Base.mapfoldr(abs2, -, 2:5; init=10) == -4
+@test @inferred(mapfoldr(x -> x + 1, (x, y) -> (x, y...), (1, 2.0, '3');
+ init = ())) == (2, 3.0, '4')
 
 @test foldr((x, y) -> ('⟨' * x * '|' * y * '⟩'), "λ 🐨.α") == "⟨λ|⟨ |⟨🐨|⟨.|α⟩⟩⟩⟩" # issue #31780
 let x = rand(10)