How can I create a custom error function similar to fmt.Sprintf using fmt.Errorf?

Formatted Error Messages with fmt.Errorf

Initial Problem:

You sought to construct a custom version of errors.New that parallels the input parameters of fmt.Sprintf. However, when you implemented this function:

<code class="go">func NewError(format string, a ...interface{}) error {
    return errors.New(fmt.Sprintf(format, a))
}</code>

You encountered an issue where 'a' became a solitary array parameter in NewError(). This resulted in fmt.Sprintf inadequately substituting just one argument into your format string.

Solution:

The obstacle you encountered stems from the absence of ... (the ellipsis) after the 'a' parameter in your function declaration. According to the Go specification, this omission hinders your code from correctly handling the variable number of arguments.

fmt.Errorf to the Rescue

Fortuitously, fmt.Errorf already features the desired functionality that you intended to implement:

<code class="go">func Errorf(format string, a ...interface{}) error {
    return errors.New(Sprintf(format, a...))
}</code>

By appending the ellipsis, you enable fmt.Errorf to deftly interpret 'a' as a variable number of arguments, skillfully catering to the needs of your formatted error messages.

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