preserve block types in similar for BlockArray (#284)

Author: jishnub

src/blockarray.jl

@@ -369,6 +369,8 @@ end
 @inline Base.similar(block_array::Type{<:AbstractArray{T}}, axes::Tuple{Union{AbstractUnitRange{Int},Integer},BlockedUnitRange,Vararg{Union{AbstractUnitRange{Int},Integer}}}) where T =
     BlockArray{T}(undef, map(to_axes,axes))
 
+@inline Base.similar(B::BlockArray, ::Type{T}) where {T} = mortar(similar.(blocks(B), T))
+
 const OffsetAxis = Union{Integer, UnitRange, Base.OneTo, Base.IdentityUnitRange}
 
 # avoid ambiguities