I met a great switch statement

I met a great switch statement

I came across this code in a Java refactoring project.

switch ( cmd ) {
    case 0: 
        //Process A
        // fall through
    case 1:
    case 2:
        //Process B
        break;
    default:
        //Process C
        break;
}

At first glance, case 0 seems to perform only processing A, but if you look closely, case 0 does not have break, so it actually does processing B as well. !!

At first, did you forget to write break? I thought, but apparently it behaved as specified.

It was a technique called fallthrough

In this way, the notation that intentionally omits break is called ** fall through **. If you look closely, you can see it in the comments.

I replaced it with the ʻif` statement

This fallthrough is a very interesting technique, but I thought it would be misleading and a breeding ground for bugs, so unfortunately I decided to replace it with the ʻif` statement.

if ( cmd == 0 ) {
    //Process A
}

if ( cmd <= 2 ) {
    //Process B
} else {
    //Process C
}

Well, was it simpler before the change? It is subtle. But I no longer have to worry about misreading.

However, if cmd is of type String, you can't write it like this. to worry.

If there is a better way to write it, please let me know.

Languages that can and cannot fall through

I was curious about the situation in other languages, so I took a quick look.

Languages that fall through if break is omitted in the switch statement

• C
• C++
• JavaScript
• PHP

Languages that get angry if you omit break in the switch statement

• C# --You can omit break if you do nothing in the case statement. --You can do something like fallthrough with goto.

Languages that explicitly specify fallthrough in the switch statement

--Perl (specify next) --Swift (specify fallthrough) --Go (specify fallthrough)

A language that has a syntax similar to the switch statement but cannot fallthrough

--Ruby (case statement) --Scala (match statement) --Kotlin (when statement)

Languages that do not have a syntax equivalent to the switch statement

• Python

Language in which all blocks that meet the conditions are executed

• PowerShell --Fall through is not possible. --All blocks that meet the conditions are executed. --You can use break to censor it.

It depends on the language! I learned a lot.