Add FieldArray from StaticArrays

Project.toml

@@ -1,6 +1,6 @@
 name = "StaticArraysCore"
 uuid = "1e83bf80-4336-4d27-bf5d-d5a4f845583c"
-version = "1.0.1"
+version = "1.1.0"
 
 [compat]
 julia = "1.6"

src/StaticArraysCore.jl

@@ -3,6 +3,7 @@ module StaticArraysCore
 export SArray, SMatrix, SVector
 export MArray, MMatrix, MVector
 export SizedArray, SizedMatrix, SizedVector
+export FieldArray, FieldMatrix, FieldVector
 
 """
     abstract type StaticArray{S, T, N} <: AbstractArray{T, N} end
@@ -269,4 +270,118 @@ const SizedVector{S,T} = SizedArray{Tuple{S},T,1,1}
 
 const SizedMatrix{S1,S2,T} = SizedArray{Tuple{S1,S2},T,2}
 
+# FieldArray
+
+"""
+    abstract FieldArray{N, T, D} <: StaticArray{N, T, D}
+
+Inheriting from this type will make it easy to create your own rank-D tensor types. A `FieldArray`
+will automatically define `getindex` and `setindex!` appropriately. An immutable
+`FieldArray` will be as performant as an `SArray` of similar length and element type,
+while a mutable `FieldArray` will behave similarly to an `MArray`.
+
+Note that you must define the fields of any `FieldArray` subtype in column major order. If you
+want to use an alternative ordering you will need to pay special attention in providing your
+own definitions of `getindex`, `setindex!` and tuple conversion.
+
+If you define a `FieldArray` which is parametric on the element type you should
+consider defining `similar_type` as in the `FieldVector` example.
+
+
+# Example
+
+    struct Stiffness <: FieldArray{Tuple{2,2,2,2}, Float64, 4}
+        xxxx::Float64
+        yxxx::Float64
+        xyxx::Float64
+        yyxx::Float64
+        xxyx::Float64
+        yxyx::Float64
+        xyyx::Float64
+        yyyx::Float64
+        xxxy::Float64
+        yxxy::Float64
+        xyxy::Float64
+        yyxy::Float64
+        xxyy::Float64
+        yxyy::Float64
+        xyyy::Float64
+        yyyy::Float64
+    end
+"""
+abstract type FieldArray{N, T, D} <: StaticArray{N, T, D} end
+
+"""
+    abstract FieldMatrix{N1, N2, T} <: FieldArray{Tuple{N1, N2}, 2}
+
+Inheriting from this type will make it easy to create your own rank-two tensor types. A `FieldMatrix`
+will automatically define `getindex` and `setindex!` appropriately. An immutable
+`FieldMatrix` will be as performant as an `SMatrix` of similar length and element type,
+while a mutable `FieldMatrix` will behave similarly to an `MMatrix`.
+
+Note that the fields of any subtype of `FieldMatrix` must be defined in column
+major order unless you are willing to implement your own `getindex`.
+
+If you define a `FieldMatrix` which is parametric on the element type you
+should consider defining `similar_type` as in the `FieldVector` example.
+
+# Example
+
+    struct Stress <: FieldMatrix{3, 3, Float64}
+        xx::Float64
+        yx::Float64
+        zx::Float64
+        xy::Float64
+        yy::Float64
+        zy::Float64
+        xz::Float64
+        yz::Float64
+        zz::Float64
+    end
+
+ Note that the fields of any subtype of `FieldMatrix` must be defined in column major order.
+ This means that formatting of constructors for literal `FieldMatrix` can be confusing. For example
+
+    sigma = Stress(1.0, 2.0, 3.0,
+                   4.0, 5.0, 6.0,
+                   7.0, 8.0, 9.0)
+
+    3×3 Stress:
+     1.0  4.0  7.0
+     2.0  5.0  8.0
+     3.0  6.0  9.0
+
+will give you the transpose of what the multi-argument formatting suggests. For clarity,
+you may consider using the alternative
+
+    sigma = Stress(SA[1.0 2.0 3.0;
+                      4.0 5.0 6.0;
+                      7.0 8.0 9.0])
+"""
+abstract type FieldMatrix{N1, N2, T} <: FieldArray{Tuple{N1, N2}, T, 2} end
+
+"""
+    abstract FieldVector{N, T} <: FieldArray{Tuple{N}, 1}
+
+Inheriting from this type will make it easy to create your own vector types. A `FieldVector`
+will automatically define `getindex` and `setindex!` appropriately. An immutable
+`FieldVector` will be as performant as an `SVector` of similar length and element type,
+while a mutable `FieldVector` will behave similarly to an `MVector`.
+
+If you define a `FieldVector` which is parametric on the element type you
+should consider defining `similar_type` to preserve your array type through
+array operations as in the example below.
+
+# Example
+
+    struct Vec3D{T} <: FieldVector{3, T}
+        x::T
+        y::T
+        z::T
+    end
+
+    StaticArrays.similar_type(::Type{<:Vec3D}, ::Type{T}, s::Size{(3,)}) where {T} = Vec3D{T}
+"""
+abstract type FieldVector{N, T} <: FieldArray{Tuple{N}, T, 1} end
+
 end # module