When Should You Choose %d Over %v for Printing Variables in Go?

Avoiding Overreliance on %v for Printing Variables

While %v offers a versatile way to print both integers (%d) and strings (%s), using it exclusively may have unintended consequences.

Default Value Formatting vs. Precise Type Formatting

%d explicitly instructs the fmt package to print integers in base 10. In contrast, %v relies on the default formatting method, which can vary based on the type being printed.

Stringer Interface Implementation Override

If an object implements the fmt.Stringer interface and provides a custom String() method, %v will prioritize that method over the default formatting. This can lead to unexpected results if you intend to print integers as numbers and not as the custom string representation.

Example:

type MyInt int

func (mi MyInt) String() string {
    return fmt.Sprintf("*%d*", int(mi))
}

func main() {
    mi := MyInt(2)
    fmt.Printf("%d %v", mi, mi)
}

Output:

2 *2*

Recommendations:

• Use %d specifically for integers to ensure accurate numeric representations.
• Use %v when printing objects where a customized string representation is expected.
• Avoid relying solely on %v to maintain precision and readability in your code.

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