make BlockedSparse immutable, add note why other types must be mutable

NEWS.md

@@ -1,3 +1,7 @@
+MixedModels v4.34.0 Release Notes
+==============================
+- `BlockedSparse` is now immutable. [#815]
+
 MixedModels v4.33.0 Release Notes
 ==============================
 - `LikelihoodRatioTest` now extends `StatsAPI.HypothesisTest` and provides a method for `StatsAPI.pvalue`. [#814]
@@ -617,3 +621,4 @@ Package dependencies
 [#802]: https://github.com/JuliaStats/MixedModels.jl/issues/802
 [#810]: https://github.com/JuliaStats/MixedModels.jl/issues/810
 [#814]: https://github.com/JuliaStats/MixedModels.jl/issues/814
+[#815]: https://github.com/JuliaStats/MixedModels.jl/issues/815

Project.toml

@@ -1,7 +1,7 @@
 name = "MixedModels"
 uuid = "ff71e718-51f3-5ec2-a782-8ffcbfa3c316"
 author = ["Phillip Alday <me@phillipalday.com>", "Douglas Bates <dmbates@gmail.com>"]
-version = "4.33.0"
+version = "4.34.0"
 
 [deps]
 Arrow = "69666777-d1a9-59fb-9406-91d4454c9d45"

src/Xymat.jl

@@ -104,6 +104,9 @@ Typically, an `FeMat` represents the fixed-effects model matrix with the respons
 Upon construction the `xy` and `wtxy` fields refer to the same matrix
 """
 mutable struct FeMat{T,S<:AbstractMatrix} <: AbstractMatrix{T}
+    # XXX This struct must be mutable, because in the unweighted
+    # case wtxy === xy and we allow users to reweight posthoc,
+    # at which point wtxy is replaced by a new matrix
     xy::S
     wtxy::S
 end

src/arraytypes.jl

@@ -60,7 +60,7 @@ A `SparseMatrixCSC` whose nonzeros form blocks of rows or columns or both.
 
 The only time these are created are as products of `ReMat`s.
 """
-mutable struct BlockedSparse{T,S,P} <: AbstractMatrix{T}
+struct BlockedSparse{T,S,P} <: AbstractMatrix{T}
     cscmat::SparseMatrixCSC{T,Int32}
     nzsasmat::Matrix{T}
     colblkptr::Vector{Int32}

src/remat.jl

@@ -18,6 +18,9 @@ A section of a model matrix generated by a random-effects term.
 - `scratch`: a `Matrix{T}`
 """
 mutable struct ReMat{T,S} <: AbstractReMat{T}
+    # XXX This struct must be mutable, because in the unweighted
+    # case wtz === z and we allow users to reweight posthoc,
+    # at which point wtxy is replaced by a new matrix
     trm::Any
     refs::Vector{Int32}
     levels::Any