Is it possible to break out of a lambda?

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Hey Everyone,

Is it possible to break out of a lambda? The reason why I am wondering is that when I get in to the if statement The functionality of what I am trying to accomplish is complete therefore I do not need to continue iterating through the vector.

Here is the code I am currently working on:

C#

std::for_each(records_.begin(), records_.end(),[&id, &updateRecord](Record & record)
{
        bool isFound = false;
        isFound = record.get_record().find(id) == 2;
        if (isFound)
        {
                record.set_record(updateRecord);
                //I want to break out of the lambda right here.
                return;
        }
});

Thanks for your time everyone,
Robbie.

Posted 22-Jan-11 14:31pm

RobNO

Updated 23-Jan-11 7:24am

Henry Minute

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Comments

Sergey Alexandrovich Kryukov 22-Jan-11 20:37pm

Why do you call this "lambda"?

RobNO 22-Jan-11 20:40pm

Refer to link: http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions

Emilio Garavaglia 23-Jan-11 2:51am

The question from SA not "improper", it is the OP question the is malposed. He can break out the lambda (with a return statement!). What it cannot do is breaking the for_each internal loop, since it is not designed to be broken. Actually what he did is not "a lambda", is a "for_each over a lambda", while he's probably looking a for_each_until or similar

RobNO 23-Jan-11 13:00pm

My bad, I am just a college student a year in...

2 solutions

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Nish Nishant · Accepted Answer · 2011-01-22T14:34:00

Solution 1

Very good S.O. thread on this same topic:

http://stackoverflow.com/questions/760221/breaking-in-stdfor-each-loop[^]

Posted 22-Jan-11 14:34pm

Nish Nishant

Comments

RobNO 22-Jan-11 20:51pm

Ill accept the answer to this response. An iterator would work just as well but I do think there needs to eventually be away to break out of the function.

Thanks for your time,
RobNO.

Nish Nishant 22-Jan-11 20:55pm

I agree, perhaps a future version will have a for_each_if or for_each_until implementation.

Aescleal · Accepted Answer · 2011-01-23T07:11:00

The reason you're having the problem is that std::for_each is meant to traverse the entire range you supply to it and not break. If you really want something to be able to terminate early you can do it with std::find_if provided you change your lambda to be a boolean predicate (which is a fairly trivial change):

[&id, &updateRecord](Record & record)->bool
{
    if( record.get_record().find(id) == 2 )
    {
        record.set_record(updateRecord);
        return true;
    }
    return false;
}

You might want to rename find_if as well to show that you're not actually trying to find something, just iterating until a condition.

Cheers,

Ash

Edit: Such a trivial change that I messed it up!

Is it possible to break out of a lambda?

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Is it possible to break out of a lambda?

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