allow arbitrary functions in map

base/reshapedarray.jl

@@ -376,6 +376,5 @@ function merge_adjacent_dim(apsz::Dims{N}, apst::Dims{N}, n::Int = 1) where {N}
     return sz, st, n
 end
 
-## ReshapedArray eltype conversion
-
-map(::Type{T}, R::ReshapedArray) where {T} = ReshapedArray(map(T, parent(R)), R.dims, R.mi)
+## ReshapedArrays may forward a mapped function to the parent
+map(f, R::ReshapedArray) = ReshapedArray(map(f, parent(R)), R.dims, R.mi)

test/abstractarray.jl

@@ -2051,7 +2051,9 @@ end
     test_unsetindex(MyMatrixUnsetIndexLinInds)
 end
 
-@testset "eltype conversion for ReshapedArray" begin
+@testset "map on a ReshapedArray (PR #40678)" begin
+    # Ranges have special map methods for eltype conversion
+    # reshaped ranges may utilize these
     r = 1:4
     R = reshape(r, 2, 2)
     for T in [Float64, BigInt]
@@ -2061,11 +2063,20 @@ end
         @test parent(S) isa AbstractRange
     end
 
-    # a more complicated case
+    # in general for Arrays, map(f, R) and map(x -> f(x), R) should behave identically
+    # and the result should match map(f, collect(R))
     R = reshape(reinterpret(Float64, ComplexF64[i for i = 1:4]), 1, :)
-    for T in [Int, BigInt]
-        S = map(T, R)
+    C = collect(R)
+    for T in [Int, BigInt], f in [T, x -> T(x)]
+        S = map(f, R)
         @test eltype(S) == T
         @test S == R
+        @test S == map(f, C)
+    end
+
+    R = reshape(1:4, 4, 1)
+    for f in [CartesianIndex, x -> CartesianIndex(x)]
+        RR = map(f, R)
+        @test RR == map(f, collect(R))
     end
 end