Add similar_type

Project.toml

@@ -1,6 +1,6 @@
 name = "StaticArraysCore"
 uuid = "1e83bf80-4336-4d27-bf5d-d5a4f845583c"
-version = "1.2.0"
+version = "1.3.0"
 
 [compat]
 julia = "1.6"

src/StaticArraysCore.jl

@@ -389,4 +389,26 @@ abstract type FieldVector{N, T} <: FieldArray{Tuple{N}, T, 1} end
 struct StaticArrayStyle{N} <: Base.Broadcast.AbstractArrayStyle{N} end
 StaticArrayStyle{M}(::Val{N}) where {M,N} = StaticArrayStyle{N}()
 
+"""
+    similar_type(static_array)
+    similar_type(static_array, T)
+    similar_type(array, ::Size)
+    similar_type(array, T, ::Size)
+
+Returns a constructor for a statically-sized array similar to the input array
+(or type) `static_array`/`array`, optionally with different element type `T` or size
+`Size`. If the input `array` is not a `StaticArray` then the `Size` is mandatory.
+
+This differs from `similar()` in that the resulting array type may not be
+mutable (or define `setindex!()`), and therefore the returned type may need to
+be *constructed* with its data.
+
+Note that the (optional) size *must* be specified as a static `Size` object (so the compiler
+can infer the result statically).
+
+New types should define the signature `similar_type(::Type{A},::Type{T},::Size{S}) where {A<:MyType,T,S}`
+if they wish to overload the default behavior.
+"""
+function similar_type end
+
 end # module