!$a == 'hello' casts $a to a (negated) boolean and compares that to a string. That may be faster, since it's easier to decide than actually comparing two strings. It'll also give you wrong results. What you need to compare against is !($a == 'hello'), which I would guess is about equal in time taken.
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!$a == 'hello'将$a转换为（否定的）布尔值并将其与字符串进行比较。这可能会更快，因为它比实际比较两个字符串更容易做出决定。它还会给你错误的结果。您需要比较的是!($a == 'hello')，我猜它所花费的时间大约相等。!$a == 'hello'casts$ato a (negated) boolean and compares that to a string. That may be faster, since it's easier to decide than actually comparing two strings. It'll also give you wrong results. What you need to compare against is!($a == 'hello'), which I would guess is about equal in time taken.