setindex! for non-isbits MArrays

Implement this for the sake of people using MArray in generic code, even
though it's unlikely to be fast.

Author: c42f

src/MArray.jl

@@ -94,9 +94,14 @@ end
     if isbitstype(T)
         GC.@preserve v unsafe_store!(Base.unsafe_convert(Ptr{T}, pointer_from_objref(v)), convert(T, val), i)
     else
-        # This one is unsafe (#27)
-        # unsafe_store!(Base.unsafe_convert(Ptr{Ptr{Nothing}}, pointer_from_objref(v.data)), pointer_from_objref(val), i)
-        error("setindex!() with non-isbitstype eltype is not supported by StaticArrays. Consider using SizedArray.")
+        # This is inherently slow because we've got to rebuild a new Tuple to
+        # reassign to data.v.
+        #
+        # However it seems not possible to make fast without having some kind
+        # of mutable pseudo-container which is inlined as a part of the parent
+        # struct such that you can't access it separately. (A mutable
+        # FieldArray achieves this, but can't be parameterized on the size.)
+        @inbounds v.data = setindex(v.data, val, i)
     end
 
     return val

test/MArray.jl

@@ -142,9 +142,12 @@
         @test_throws BoundsError setindex!(mm, 4, -1)
         @test_throws BoundsError setindex!(mm, 4, 82)
 
-        # setindex with non-elbits type
-        m = MArray{Tuple{2,2,2}, String}(undef)
-        @test_throws ErrorException setindex!(m, "a", 1, 1, 1)
+        # setindex with non-bits eltype
+        m = fill("a", MMatrix{2,2, String})
+        m[1,1] = "b"
+        m[1,2] = "c"
+        @test m == ["b" "c";
+                    "a" "a"]
     end
 
     @testset "promotion" begin