Merge pull request #42399 from JuliaLang/ksh/copytodoctest

Add a doctest for copyto with CartesianIndices

Author: kshyatt

base/multidimensional.jl

@@ -1127,6 +1127,25 @@ end
 
 Copy the block of `src` in the range of `Rsrc` to the block of `dest`
 in the range of `Rdest`. The sizes of the two regions must match.
+
+# Examples
+```jldoctest
+julia> A = zeros(5, 5);
+
+julia> B = [1 2; 3 4];
+
+julia> Ainds = CartesianIndices((2:3, 2:3));
+
+julia> Binds = CartesianIndices(B);
+
+julia> copyto!(A, Ainds, B, Binds)
+5×5 Matrix{Float64}:
+ 0.0  0.0  0.0  0.0  0.0
+ 0.0  1.0  2.0  0.0  0.0
+ 0.0  3.0  4.0  0.0  0.0
+ 0.0  0.0  0.0  0.0  0.0
+ 0.0  0.0  0.0  0.0  0.0
+```
 """
 copyto!(::AbstractArray, ::CartesianIndices, ::AbstractArray, ::CartesianIndices)