[Containers] fix sum of DenseAxisArray that doesn't support zero(T) (#4097)

Author: odow

src/Containers/DenseAxisArray.jl

@@ -854,11 +854,13 @@ function Base.summary(io::IO, x::DenseAxisArrayView)
     return print(io, "view(::DenseAxisArray, ", join(x.axes, ", "), "), over")
 end
 
+struct _InitNotProvided end
+
 function Base.sum(
     f::F,
     x::Union{DenseAxisArray{T},DenseAxisArrayView{T}};
     dims = Colon(),
-    init = zero(T),
+    init = _InitNotProvided(),
 ) where {F<:Function,T}
     if dims != Colon()
         return error(
@@ -867,7 +869,11 @@ function Base.sum(
             "for-loop summation instead.",
         )
     end
-    return sum(f(xi) for xi in x; init)
+    if init == _InitNotProvided()
+        return sum(f(xi) for xi in x)
+    else
+        return sum(f(xi) for xi in x; init)
+    end
 end
 
 function Base.sum(x::Union{DenseAxisArray,DenseAxisArrayView}; kwargs...)

test/Containers/test_DenseAxisArray.jl

@@ -992,15 +992,31 @@ end
 
 function test_sum_init()
     x = Containers.@container([i in Int[]], i)
-    @test sum(x) == 0
+    if VERSION < v"1.7"
+        @test sum(x) == 0
+    else
+        @test_throws ArgumentError sum(x)
+    end
     @test sum(x; init = 1) == 1
     y = Containers.@container([i in BigInt[]], i)
-    y_1 = sum(y)
-    @test y_1 == 0
-    @test y_1 isa BigInt
+    if VERSION < v"1.7"
+        @test sum(y) == 0
+    else
+        @test_throws ArgumentError sum(y)
+    end
     y_2 = sum(y; init = 0)
     @test y_2 === 0
     return
 end
 
+function test_sum_init_any()
+    x = Containers.@container([i in Any[]], i)
+    if VERSION < v"1.7"
+        @test_throws MethodError sum(x)
+    else
+        @test_throws ArgumentError sum(x)
+    end
+    return
+end
+
 end  # module

test/Containers/test_macro.jl

@@ -279,4 +279,13 @@ function test_trailing_semicolon()
     return
 end
 
+function test_init_issue_4096()
+    x = Containers.DenseAxisArray(Any[1, 2, 3], Int[1, 2, 3])
+    @test sum(x) == 6
+    @test (@allocated sum(x)) == 0
+    @test sum(x; init = 0) == 6
+    @test (@allocated sum(x; init = 0)) == 0
+    return
+end
+
 end  # module