Making custom loops?

Roy S

I have a certain nesting of loops, something similar to this:

for (int i = 0; i < 10; i++)
{
        for (int j = 0; j < 10; j++)
        {
                for (int k = i + j; ;k += i + j)
                {
                        doing stuff here...
                }
        }
}

Returning all over my project. the only thing changing is what I do inside the loops.

Is there a way to put the whole loop thing somewhere else and just tell what needs to be done in the loop? I was thinking of using something like this:

public void Main()
{
        CostumLoop(i =>
        {
                doing stuff here...
        });
}

public void CostumLoop(Action<int> doStuff)
{
        for (int i = 0; i < 10; i++)
        {
                for (int j = 0; j < 10; j++)
                {
                        for (int k = i + j; ;k += i + j)
                        {
                                doStuff(k);
                        }
                }
        }
}

But then I can't use any breaks or continue etc (which I actually need)... Is there maybe a way of telling that the break in de lambda is going to executed inside a loop and that it shouldn't give an error?

Any ideas?

8 Replies

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Sam Hobbs15y ago
Accepted answer
It must be possible. It seems totally possible to me.

Yeah this value type and reference type stuff is confusing. You are probably correct that the boolean was not changed because of the way it was passed. You solve that by putting "ref" with the parameter.

I assume that you need break and continue only for the innermost loop. I seldom use either one so I might get confused about which is which. For me, I would usually make a function that I call to do the processing for each iteration and then the return is the equivalent of .... let's see; the equivalent of continue, correct? So if you use a delegate to specify a function to execute for each iteration, then the return is the equivalent of the continue.

So you need a boolean to indicate the equivalent of a break; that the current innermost loop is to stop. A for loop is like a while except the for loop has the intializer and the iteration as well as a condition. So you could add a boolean to the condition in the innermost for loop and that can be used to stop the current loop. I hope you understand.

Does that satisfy your requirements?

One suggestion. Instead of passing many parameters, you could define a class or structure that you use to pass some of the parameters. It might make things easier to work with.
Vulpes15y ago
If you're thinking here of anonymous methods, then they have exactly the same problems as lambdas vis-a-vis capturing outer variables.

A simple delegate can, of course, invoke one or several methods simultaneously. But, if you just want to invoke a single method, then you may as well call it directly using the appropriate arguments.
Sam Hobbs15y ago
Delegates can be used without Lambdas, correct? So just get it working without Lambdas and then later try Lambdas.
Vulpes15y ago
The reason why the bool passed within the lambda didn't appear to change anything you did in the loop may be nothing to do with passing structs by value or reference etc.

If the bool is a 'captured variable' i.e. a local variable or parameter of the method in which the lambda is defined, then its lifetime is extended to that of the lambda itself and its value is not its value when it was captured but its value when the lambda is actually invoked. So, if the value of the bool has been changed in the meantime, then that's the value that will get passed.

This can lead to some subtle and hard to find bugs.

In the background, the C# compiler generates a hidden class and the captured variables become fields of this hidden class. It's no wonder then that lambdas are slow compared to 'normal' code.

If you're going to encapsulate your loops within a generic method to which various parameters are passed (however packaged) to control iteration ranges and break or continue points, then I'd avoid using lambdas altogether.

You might still end up with code which is difficult to maintain but at least it should be as bug-free as your original loops and only slightly less performant.
Roy S15y ago
It was just a quick example, the real loop is a bit different.

This is an actual example of one of those loops:

for (int i = -8; i < 9; i += 8)
{
        for (int j = -1; j < 2; j++)
        {
                if (i != 0 || j != 0)
                {
                        for (int k = position + i + j; k >= 0 && k < 64 && 2 * (k & 7) != 7 - 7 * j && !board[k].CanBeMovedBy(owner); k += i + j)
                        {
                                if (!(board[k] is Empty))
                                {
                                        if (board[k] is Queen || board[k] is Rook && i * j == 0 || board[k] is Bishop && i * j != 0)
                                        {
                                                return true;
                                        }
                                        else
                                        {
                                                break;
                                        }
                                }
                        }
                }
        }
}
theLizard15y ago
        for (int i = 0; i < 10; i++)
        {
                for (int j = 0; j < 10; j++)
                {
                        for (int k = i + j; ;k += i + j)
                        {
                                doStuff(k);
                        }
                }
        }

What are you trying to do here?

for (int k = i + j; ;k += i + j)
                        {
                                doStuff(k);
                        }

K is always 0, what does doStuf(k) do to break out of the loop at this point
Roy S15y ago
I tried to put a boolean as one of the parameters in the Action delegate but it didn't really work. Whatever I did to that boolean in the lambda thing didn't change to the actual boolean I gave in the loop (I think it's because boolean is a struct and is passed by value instead of reference or something like that).

Making my own delegate with boolean as return value worked but after testing, it seemed about 7 times slower than the original code...

so yes you're right it's too much of a mess and also too slow. I'll have to do it with the old way and maybe make a snippet to make it easier.
Vulpes15y ago
The only way to do it would be to pass some bool parameters to the CostumLoop method which, if true, would generate break or continue statements in the appropriate places.

You couldn't put the break or continue statements in the body of the lambda itself as you'd then get compiler errors because there were no loops to break out of or continue!

However, my feeling is that you'd probably end up with a horrible mess and, except in a simple case with no breaks or continues, it would be better just to live with the loops you've already got and forget about using lambdas.