Chained Control Flow Statements: break [, break]... [,continue]

[Caracrist]

The concept is to allow multiple break statements and an optional continue operation within a single line, as shown below:

while (cond1) // returns here from: break, continue
{
    while (cond2)
    {
        if (cond3)
        {
            break, break; // break from the inner and outer loop
        }
        else if (cond4)
        {
            break, continue; // break from the inner loop and continue in the outer loop
        }
    }
    // this code is reached only if !cond2
}
// code reached from "break, break" or if !cond1

while (cond1) // returns here from: break, continue
{
    switch (item)
    {
        case value1:
            break, break; // break from the switch and break outer loop
        case value2:
            break, continue; // break from the switch and continue in the outer loop
        default:
            break;
    }
    // this code is reached only if default
}
// code reached from "break, break" or if !cond1

The break statements can exit loops or switch case blocks. The number of break statements is limited by the number of enclosing scopes, while the continue statement can only appear once and must be the last in the sequence.

The formal definition is (see subj):

break [, break]... [, continue]

This means that within a block of code, multiple break statements and an optional continue can be used at the end. None are mandatory, ensuring full backward compatibility.

Typically, alternatives to this approach involve managing multiple flags, akin to a state machine spread across local variables, combined with many if statements to handle conditions in the right place. This can complicate both the code and its readability.

Additionally, since each statement (break, continue) is a distinct word, it can be highlighted in the IDE, showing its relation to the corresponding block (for, foreach, while, switch, do). During debugging, these statements can be executed one by one, similar to how execution is handled inside for (statements), with each part of the line being highlighted independently.

[zhenkas]

Elegant! I want it in c++ too!

[emamontov]

This kind of feature that everybody need, but nobody knows that.
+Upvoted

[HaloFour]

See:

#6634

[timcassell]

I do prefer labeled loops (that would also work with continue).

[emamontov]

There is a discussion while here is the proposal in completed form.

[HaloFour]

I personally prefer the labels, it's very clear exactly where the flow will go. break, break; is just as brittle as break 2; when it comes to potential refactoring.

Either way, the language team hasn't expressed much interest here as goto with a label is sufficient.

[VaronisContributor]

goto with a label is anti-pattern ...

[koszeggy]

goto with a label is anti-pattern ...

...which is a big misunderstanding. goto can be dangerous in C/C++ but in C# it is much more restricted (e.g. you cannot just jump out of a finally block, or to code points where variables would not be initialized, not mentioning jumping into another method, or doing other crazy things that could even corrupt the stack).

The runtime itself also uses a lot of goto, especially on performance critical paths.

When that's the best tool, just use it. Don't afraid of others who have gotophobia.

[CyrusNajmabadi]

Proposal started here: https://github.com/dotnet/csharplang/blob/main/proposals/labeled-break-continue.md
Championed Issue here: #9875
Discussion here: #9876

Closing this out to move discussion there.