make extrema with dims inferrable (#39321)

fixes #39281 (cherry picked from commit caeacef)
JuliaLang · Jan 20, 2021 · 14ba71b · 14ba71b
1 parent 9719e6e
commit 14ba71b
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diff --git a/base/multidimensional.jl b/base/multidimensional.jl
@@ -1698,9 +1698,9 @@ extrema(f, A::AbstractArray; dims=:) = _extrema_dims(f, A, dims)
 _extrema_dims(f, A::AbstractArray, ::Colon) = _extrema_itr(f, A)
 
 function _extrema_dims(f, A::AbstractArray, dims)
-    sz = [size(A)...]
+    sz = size(A)
     for d in dims
-        sz[d] = 1
+        sz = setindex(sz, 1, d)
     end
     T = promote_op(f, eltype(A))
     B = Array{Tuple{T,T}}(undef, sz...)

diff --git a/test/reduce.jl b/test/reduce.jl
@@ -608,3 +608,6 @@ x = [j+7 for j in i]
         Iterators.flatten((1:2, 3:4)),
     ) == (1, 4)
 end
+
+# issue #39281
+@test @inferred(extrema(rand(2), dims=1)) isa Vector{Tuple{Float64,Float64}}