有条件地分配PHP值 [英] Conditionally assigning PHP values
问题描述
在非常常见的情况下,根据表达式的结果为变量赋值,我是三元运算符的爱好者:
$ foo = $ bar? $ a:b;
但是,如果$ bar是一个相对昂贵的操作,我想将$ bar的结果赋给$ foo如果结果为真,则效率低下:
$ foo = SomeClass :: bigQuery()吗? SomeClass :: bigQuery():new EmptySet();
一个选项是:
$ foo =($ result = SomeClass :: bigQuery())吗? $ result:newEmptySet();
但是我宁愿没有多余的 $ result
坐在内存中。
我最好的选择是:
$ foo =($ foo = SomeClass :: bigQuery())吗? $ foo:新的EmptySet();
或者,没有三元运算符:
if(!$ foo = SomeClass :: bigQuery())$ foo = new EmptySet();
或者,如果程序流运算符不是您的风格:
($ foo = SomeClass :: bigQuery())|| ($ foo =新的EmptySet());
这么多的选择,没有一个真的令人满意。您将使用哪一个,而我在这里确实遗漏了一些明显的东西? :
$ x = cheaper()?:$ default;
请参见文档:
自PHP 5.3起,可以省略三元运算符的中间部分。
表达式expr1?:expr3
如果expr1
expr1 >的值为TRUE
,否则为expr3
。
For the very common case of assigning a value to a variable based on the outcome of an expression I'm a fan of ternary operators:
$foo = $bar ? $a : b;
However, if $bar is a relatively expensive operation and I want to assign the result of $bar to $foo if the result is truthy, this is inefficient:
$foo = SomeClass::bigQuery() ? SomeClass::bigQuery() : new EmptySet();
One option is:
$foo = ($result = SomeClass::bigQuery()) ? $result : new EmptySet();
But I'd rather not have the extra $result
sitting in memory.
The best option I've got is:
$foo = ($foo = SomeClass::bigQuery()) ? $foo : new EmptySet();
Or, without ternary operators:
if(!$foo = SomeClass::bigQuery()) $foo = new EmptySet();
Or, if program flow operators are not your style:
($foo = SomeClass::bigQuery()) || ($foo = new EmptySet());
So many options, non of them really satisfactory. Which would you use, and am I missing something really obvious here?
PHP 5.3 introduced a new syntax to solve exactly this problem:
$x = expensive() ?: $default;
See the documentation:
Since PHP 5.3, it is possible to leave out the middle part of the ternary operator.
Expressionexpr1 ?: expr3
returnsexpr1
ifexpr1
evaluates toTRUE
, andexpr3
otherwise.
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