Unfortunately, once you start writing general predicates describing the values you would like to handle within a particular function body, it becomes easy to create ambiguous conditions.
There is more than one function that matches and none of the matches is clearly best. This case is also an error; the call is ambiguous .
存在多个与实参匹配的函数，但没有一个是明显的最佳选择。这种情况也是，该调用具有二义性。
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If after looking at each argument there is no single function that is preferable, then the call is in error. The compiler will complain that the call is ambiguous.