function map_stored_blocks(f, a::AbstractArray)

# TODO: Implement this as:

# ```julia

# mapped_blocks = SparseArraysInterface.map_stored(f, blocks(a))

# BlockSparseArray(mapped_blocks, axes(a))

# ```

# TODO: `block_stored_indices` should output `Indices` storing

# the stored Blocks, not a `Dictionary` from cartesian indices

# to Blocks.

bs = collect(eachblockstoredindex(a))

ds = map(b -> f(@view(a[b])), bs)

# We manually specify the block type using `Base.promote_op`

# since `a[b]` may not be inferrable. For example, if `blocktype(a)`

# is `Diagonal{Float64,Vector{Float64}}`, the non-stored blocks are `Matrix{Float64}`

# since they can't necessarily by `Diagonal` if there are rectangular blocks.

mapped_blocks = Dictionary{eltype(bs),eltype(ds)}(bs, ds)

# TODO: Use `similartype(typeof(a), eltype(eltype(mapped_blocks)))(...)`.

return BlockSparseArray(mapped_blocks, axes(a))

end