


What is the purpose of the fallthrough keyword in golang switch statements
Jul 13, 2025 am 03:03 AMIn Go, you use fallthrough in a switch statement to explicitly continue execution into the next case. 1. It allows shared logic across multiple cases without duplication. 2. Unlike C or Java, Go breaks by default to prevent accidental bugs. 3. fallthrough transfers control to the next case regardless of condition. 4. It must be the last line in a case block and cannot be used in default. 5. Avoid overusing it; prefer combining cases with commas or extracting functions for clarity.
In Go, the fallthrough
keyword in a switch
statement is used to explicitly allow execution to continue into the next case. Normally, once a case is matched and executed, the switch block exits. But sometimes you want multiple cases to share logic, and that’s where fallthrough
comes in.

Why would you use fallthrough?
Most programming languages with switch statements (like C or Java) automatically fall through to the next case unless you break out of it. Go takes the opposite approach — it breaks by default. This was a design decision to avoid accidental bugs from unintended fallthrough behavior.

However, there are cases where you do want to execute code from multiple cases. For example:
switch value := someFunc(); value { case 1: fmt.Println("One") case 2: fmt.Println("Two or maybe three") case 3: fmt.Println("Three") }
If value
is 2, this will print both "Two or maybe three" and "Three" because of the fallthrough
.

You might use fallthrough
when writing parsers, handling state machines, or grouping similar conditions together without duplicating code.
How does fallthrough work exactly?
When you use fallthrough
, it transfers control to the first line of the next case regardless of condition. It doesn't re-evaluate the value being switched on — it just continues executing.
Here's a simple example:
n := 2 switch n { case 1: fmt.Println("One") case 2: fmt.Println("Two") fallthrough case 3: fmt.Println("Three") default: fmt.Println("Other") }
Output:
Two Three
Even though n
is 2, the fallthrough
causes the case 3
block to run as well.
A few things to keep in mind:
fallthrough
must be the last line in a case block.- You can't use it in the
default
case. - It only moves to the immediate next case, not all remaining ones.
When should you avoid using fallthrough?
While fallthrough
can be useful, it can also make code harder to read and maintain if overused. Since it's not the default behavior in Go, someone reading your code might miss the intentional fallthrough and assume it's a bug or mistake.
It's generally better to:
- Combine cases that share logic with commas instead of fallthrough when possible.
- Extract shared logic into a helper function.
- Add a comment explaining why fallthrough is needed, especially if it's not obvious.
For example, this avoids fallthrough entirely:
switch n { case 2, 3: fmt.Println("Two or Three") }
Use fallthrough
only when it genuinely makes the logic clearer or more efficient than other approaches.
So yeah, fallthrough
gives you fine-grained control over how cases in a switch behave, but it's best reserved for specific situations where its intent is clear and justified.
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