status_with.h

// status_with.h
 
/*    Copyright 2013 10gen Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
 
#pragma once
 
#include "mongo/base/status.h"
 
namespace mongo {
 
 
/*
 * StatusWith is used to return an error or a value
 * this is designed to make exception code free cleaner by not needing as many out paramters
 * example:
  StatusWith<int> fib( int n ) {
    if ( n < 0 ) return StatusWith<int>( ErrorCodes::BadValue, "paramter to fib has to be >= 0" );
    if ( n <= 1 ) return StatusWith<int>( 1 );
    StatusWith<int> a = fib( n - 1 );
    StatusWith<int> b = fib( n - 2 );
    if ( !a.isOK() ) return a;
    if ( !b.isOK() ) return b;
    return StatusWith<int>( a.getValue() + b.getValue() );
  }
 
  * Note: the value is copied in the current implementation, so should be small (int, int*)
  *  not a vector
 */
template <typename T>
class StatusWith {
public:
    StatusWith(ErrorCodes::Error code, const std::string& reason, int location = 0)
        : _status(Status(code, reason, location)) {}
 
    explicit StatusWith(const Status& status) : _status(status) {
        // verify(( !status.isOK() ); // TODO
    }
 
    explicit StatusWith(const T& t) : _status(Status::OK()), _t(t) {}
 
    const T& getValue() const { /* verify( isOK() ); */
        return _t;
    }  // TODO
    const Status& getStatus() const {
        return _status;
    }
 
    bool isOK() const {
        return _status.isOK();
    }
 
    std::string toString() const {
        return _status.toString();
    }
 
private:
    Status _status;
    T _t;
};
}