Feature/moving error to framework

[reyoung]

Move paddle/utils/Error.h to paddle/framework/error.h.

Make new framework using paddle::Error as error type.

[typhoonzero]

Is this PR fix #2430?

[typhoonzero]

Why a shared_ptr, can ::std::string object do the job?

[reyoung]

No. Because if we using std:: string, Error will copy by value each time, which is very time-consuming.

[typhoonzero]

Well, Error object creation will do one memory operation. But after that, we'll pass error object using reference all the time, we can also use Error as return types of functions as we have return value optimization

This is the sample code from this PR:

Error __must_check foobar() {
  Error err;
  // do something.
  foo(&err);
  if (err) return err;
}

[reyoung]

We should not mainly use foo(Error* error) to return Error. __must_check will let developer force to check the return error, but foo(Error* error) does not have the same technic. So it is better to use Error __must_check foo();.

In another hand, RVO depends on compiler implementation.

[typhoonzero]

I'm thinking of two type of use case, which is already in this PR:

// single error return value
Error err = foo();
// multiple return values with Error
Error err;
ReturnValue ret;
foo(&err, &ret);
// more general uses, mostly use error as return value.
ReturnValue ret;
Error err = foo(&ret, "params");

[reyoung]

@typhoonzero By using msg_ a shared_ptr, the operator== will be fast for predefined Error.

[typhoonzero]

I see.

[helinwang]

I am not very familiar with C++ naming convention so I could be wrong: to me it seems ok() is better than isOK() (btw, maybe should be isOk rather than isOK according to Google C++ style?), "is" makes developers type two more characters, and does not provide much value in my opinion.

[reyoung]

My fault, It will be changed soon.

[reyoung]

Done.

[helinwang]

Do we need error code to specify what kind of error it is? Two errors with different error message could be the same kind of error (e.g., Error("open file failed: /tmp/foo"), Error("open file failed: /tmp/bar")).

[reyoung]

Do we need error code to specify what kind of error it is? Two errors with different error message could be the same kind of error (e.g., Error("open file failed: /tmp/foo"), Error("open file failed: /tmp/bar")).

In this case, maybe a global function bool IsNotFound(const Error& err) is need.

bool IsNotFound(const Error& err) {
   auto pattern = r"file not found: .*";
   return pattern.math(err.msg());
}

IsNotFound is slower than Error Code but it may not be a performance critical path for Paddle.

And I think the most error of Paddle should not be a dynamic string. The most error should be just a predefined const string.

const Error FileNotFound = Error("file is not found.");

Then IsNotFound should just invoke error's operator ==, and just a pointer match operation.

[reyoung]

Closed because #2646