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<?php ${" "} = "blank space"; ${"123"} = 456; var_dump(${" "},${"123"}); $a = get_defined_vars(); echo array_key_exists(" ",$a)? "Yes" : "No","\n"; echo array_key_exists("123",$a)? "Yes" : "No";
Output for 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.10, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
string(11) "blank space" int(456) Yes No
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9
string(11) "blank space" int(456) Yes Yes

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216.59 ms | 401 KiB | 306 Q