Php multi-layer array foreach reference and copy-php Tutorial

{Code...} by default, foreach is used to copy an array, which requires two times of memory. Will the performance be very low? Why should we design it like this? if the array is very large, would it be better to use the reference method? What are their advantages and disadvantages?

$ A = ["a" => ["cc" => 11], "B" => ["cc" => 22]; echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; $ I = 1; // (1) copy, $ a unchanged foreach ($ a as $ k => $ v) {$ v ['CC'] = $ I; $ I + = 1 ;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; // (2) reference foreach ($ a as $ k => & $ v) {$ v ['CC'] = $ I; $ I + = 1;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; // (3) copy foreach ($ a as $ k => $ v) {$ a [$ k] ["cc"] = $ I; $ I + = 1;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"];

By default, foreach copies an array and requires two times of memory. Will the performance be low? Why is it designed like this?
If the array is very large, is it better to use the reference method? What are their advantages and disadvantages?

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$ A = ["a" => ["cc" => 11], "B" => ["cc" => 22]; echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; $ I = 1; // (1) copy, $ a unchanged foreach ($ a as $ k => $ v) {$ v ['CC'] = $ I; $ I + = 1 ;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; // (2) reference foreach ($ a as $ k => & $ v) {$ v ['CC'] = $ I; $ I + = 1;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"]; // (3) copy foreach ($ a as $ k => $ v) {$ a [$ k] ["cc"] = $ I; $ I + = 1;} echo "\ n ". $ a ['A'] ["cc"]. ",". $ a ['B'] ["cc"];

By default, foreach copies an array and requires two times of memory. Will the performance be low? Why is it designed like this?
If the array is very large, is it better to use the reference method? What are their advantages and disadvantages?