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.