Unexpected values in range loop

Why does this code

primes := []int{2, 3, 5, 7} for p := range primes {	fmt.Println(p) }

print

0 1 2 3 

Answer

For arrays and slices, the range loop generates two values:

• first the index,
• then the data at this position.

If you omit the second value, you get only the indices.

To print the data, use the second value instead:

primes := []int{2, 3, 5, 7} for _, p := range primes {	fmt.Println(p) } 

In this case, the blank identifier (underscore) is used for the return value you're not interested in.

See 4 basic range loop (for-each) patterns for all about range loops in Go.

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