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<?php declare(strict_types=1); interface I { public function example(); } class A implements I { public function example(): int { return 123; } // compatible with I::example } class B extends A { public function example(): string { return "string"; } // compatible with I::example } function accepts_i_expects_any(I $i) { var_dump($i->example()); } accepts_i_expects_any(new B); // receives string, no problem function accepts_a_expects_int(A $a) { var_dump($a->example()); } accepts_a_expects_int(new B); // receives string, problem
Output for 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.4, 8.3.6
Fatal error: Declaration of B::example(): string must be compatible with A::example(): int in /in/TUbfJ on line 12
Process exited with code 255.
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0 Fatal error: Declaration of B::example(): string must be compatible with A::example(): int in /in/TUbfJ on line 12
Process exited with code 255.
Output for 7.2.0 - 7.2.33, 7.3.0 - 7.3.33
Fatal error: Declaration of B::example(): string must be compatible with A::example(): int in /in/TUbfJ on line 11
Process exited with code 255.
Output for 7.0.0 - 7.0.20, 7.1.1 - 7.1.25
string(6) "string" string(6) "string"
Output for 7.1.0

Process exited with code 137.
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177.33 ms | 405 KiB | 181 Q