两行代码给 PHP7 添加一个“非空合并”语法糖

<?php$a = 0;$b = $a ?: 1; # $b === 1

<?php$a = 0;$b = $a ? $a : 1; # $b === 1

|   expr '?' { zend_do_begin_qm_op(&$1, &$2 TSRMLS_CC); }    expr ':' { zend_do_qm_true(&$4, &$2, &$5 TSRMLS_CC); }    expr     { zend_do_qm_false(&$$, &$7, &$2, &$5 TSRMLS_CC); }|   expr '?' ':' { zend_do_jmp_set(&$1, &$2, &$3 TSRMLS_CC); }    expr     { zend_do_jmp_set_else(&$$, &$5, &$2, &$3 TSRMLS_CC); }

|   expr '?' expr ':' expr        { $$ = zend_ast_create(ZEND_AST_CONDITIONAL, $1, $3, $5); }|   expr '?' ':' expr        { $$ = zend_ast_create(ZEND_AST_CONDITIONAL, $1, NULL, $4); }

<?php$b = $a ?? 1;

<?php$b = isset($a) ? $a : 1;

|   expr T_COALESCE expr        { $$ = zend_ast_create(ZEND_AST_COALESCE, $1, $3); }

<?php$b = $a ?? 1 ?: 1;

<?php$b = $a ??: 1;

|   expr T_COALESCE ':' expr        { $$ = zend_ast_create(ZEND_AST_CONDITIONAL,            zend_ast_create(ZEND_AST_COALESCE, $1, $4), NULL, $4); }

$ /usr/local/php/bin/php -r "\$a = 0; echo \$a ?? 1, PHP_EOL;"0$ /usr/local/php/bin/php -r "\$a = 0; echo \$a ??: 1, PHP_EOL;"1