specialize copy

Author: jishnub

src/SDiagonal.jl

@@ -61,3 +61,5 @@ function inv(D::SDiagonal)
     check_singular(D)
     SDiagonal(inv.(D.diag))
 end
+
+Base.copy(D::SDiagonal) = Diagonal(copy(diag(D)))

test/SDiagonal.jl

@@ -123,5 +123,7 @@ using StaticArrays, Test, LinearAlgebra
 
         @test m + zero(m) == m
         @test m + zero(typeof(m)) == m
+
+        @test copy(m) === m
     end
 end