Notes

go_control_flow

3 min read

Go Control Flow

Purpose

Go provides if/else, switch, and for (the only loop keyword) for controlling execution flow. The design is intentionally minimal: no while, no do-while, no parentheses on conditions.

Implementation Notes

if / else if / else

No parentheses around the condition; braces are mandatory.

if height > 6 {
    fmt.Println("super tall")
} else if height > 4 {
    fmt.Println("tall enough")
} else {
    fmt.Println("not tall enough")
}

Short Variable Declaration in if

Declare a variable scoped to the if block only:

if length := getLength(email); length < 1 {
    fmt.Println("email is invalid")
}
// length is not accessible here

This limits scope and is idiomatic for error checks:

if err := doSomething(); err != nil {
    return err
}

switch

No break needed — cases do not fall through by default. Use fallthrough explicitly when needed.

switch os {
case "linux":
    fmt.Println("Linus Torvalds")
case "mac":
    fmt.Println("A Steve")
default:
    fmt.Println("Unknown")
}

No-condition switch (acts like an if/else chain):

switch {
case score >= 90:
    grade = "A"
case score >= 80:
    grade = "B"
default:
    grade = "F"
}

Explicit fallthrough:

case "macOS":
    fallthrough
case "Mac OS X":
    fallthrough
case "mac":
    creator = "A Steve"

for — Go’s Only Loop

Standard C-style:

for i := 0; i < 10; i++ {
    fmt.Println(i)
}

While-style (omit init and post):

n := 1
for n < 100 {
    n *= 2
}

Infinite loop (omit all three sections):

for {
    // runs forever; use break to exit
}

for range

Iterate over slices, maps, strings, and channels:

// slice — index + value
for i, v := range []string{"a", "b", "c"} {
    fmt.Println(i, v)
}
 
// map — key + value
for k, v := range myMap {
    fmt.Println(k, v)
}
 
// discard index
for _, v := range items {
    fmt.Println(v)
}

continue & break

for i := 0; i < 10; i++ {
    if i%2 == 0 {
        continue // skip even numbers
    }
    if i == 7 {
        break // stop at 7
    }
    fmt.Println(i) // 1, 3, 5
}

continue and break can be used inside for range the same way.

Trade-offs

  • There is no while keyword — for condition {} is the equivalent.
  • Switch cases do not fall through by default (opposite of C/Java); this avoids a common bug class.
  • The short init statement in if keeps the scope tight but may surprise readers unfamiliar with Go.
  • for range over a map has non-deterministic iteration order.

References

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