http://msdn.microsoft.com/en-us/library/s9cz43ek(v=vs.80).aspx
它强制文字0的类型为Single.
另请参阅:http: //msdn.microsoft.com/en-us/library/dzy06xhf.aspx有关附加的类型字符.
0!表示它是浮点数(单个)而不是整数.
typeOf 0! is Single
typeOf 0 is Integer
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