this post was submitted on 04 Jul 2023
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True or False: If a match expression doesn't match any case pattern and there's no default case, control falls through a switch statement. (learn.microsoft.com)
submitted 1 year ago by jim_stark to c/dotnet
7 comments fedilink hide all child comments
 

What does "control falls through a switch statement" mean in this context? Control just moves on to the next statement?

I thought if there is no match and a default case doesn't exist it will raise an exception. Is it not true?

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[–] [email protected] 2 points 1 year ago (1 children)

A switch statement will let control fall through. A switch expression will no, and will throw an exception (and there will also be a compiler warning that it's not exhaustive before you even run the code)

[–] jim_stark 3 points 1 year ago* (last edited 1 year ago) (1 children)

A switch statement will let control fall through.

I think even switch statement doesn't allow it because every case needs to be terminated with either break, return or raise. One needs to use case goto if one wants fall thought like behavior:

switch (x)
{
case "One":
    Console.WriteLine("One");
    goto case "Two";
case "Two":
    Console.WriteLine("One or two");
    break;
}

C# outlaws this, because the vast majority of case sections do not fall through, and when they do in languages that allow it, it’s often a mistake caused by the developer forgetting to write a break statement (or some other statement to break out of the switch). Accidental fall-through is likely to produce unwanted behavior, so C# requires more than the mere omission of a break: if you want fall-through, you must ask for it explicitly.

Programming C# 10 ~ Ian Griffiths

[–] RonSijm 3 points 1 year ago (1 children)

I think even switch statement doesn't allow it [...]

A switch statement allows fall through when the case itself doesn't have an implementation.

For example this is also considered a fall through:

        switch (x)
        {
            case "One":
            case "Two":
                Console.WriteLine("One or two");
                break;
        }
[–] jim_stark 1 points 1 year ago

TIL!!!

Thank you!