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<?php function my_callback( &$param ) {} $callback = 'my_callback'; $a = true; $b = array( $a ); $c = array( &$a ); //my_callback( true ); // Fatal error: passing a value when reference is expected. my_callback( $a ); // OK my_callback( ...$b ); // OK my_callback( ...$c ); // OK //$callback( true ); // Fatal error: passing a value when reference is expected. $callback( $a ); // OK $callback( ...$b ); // OK $callback( ...$c ); // OK call_user_func( $callback, true ); // PHP 7.1+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func( $callback, $a ); // PHP 7.1+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func( $callback, ...$b ); // PHP 5.6+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func( $callback, ...$c ); // PHP 7.0+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func_array( $callback, array( true ) ); // PHP 7.0+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func_array( $callback, array( $a ) ); // PHP 7.0+: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func_array( $callback, $b ); // PHP 5.6: Warning: Parameter 1 to my_callback() expected to be a reference, value given call_user_func_array( $callback, array( &$a ) ); // OK call_user_func_array( $callback, $c ); // OK
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