关于编译Lambda时报告返回的为void的错误

这个错误的信息是这样的：

a lambda that has been specified to have a void return type cannot return a value

报告错误的lambda的写法大概是这样：

[](int a, int b){    return a<b;};

至于为什么，看这个解释：

The C++11 standard, §5.1.2/4 states:

If a lambda-expression does not include a trailing-return-type, it is as if the trailing-return-type denotes the following type:

If the compound-statement is of the form { return expression ; } the type of the returned expression after lvalue-to-rvalue conversion (4.1), array-to-pointer conversion (4.2), and function-to-pointer conversion (4.3);

otherwise, void.