教你用两行代码给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