all: purge opaque errors from suite

[kortschak]

The ev3go/ev3dev package was easy to start with errors.New and fmt.Errorf, but it makes mechanical error handling difficult. So add three (?) error interface types and relevant implementations:

Interfaces

type ValidValuer interface {
    ValidValues() []string
}

type ValidRanger interface {
    ValidRange() (min, max int)
}

type ValidDurationRanger interface {
    ValidDurationRange() (min, max time.Duration)
}

Implementation example

type NegativeDuration time.Duration

func (d NegativeDuration) Error() string {
    if d >= 0 {
        panic(fmt.Sprintf("ev3dev: invalid negative duration: %v", d))
    }
    return fmt.Sprintf("ev3dev: invalid duration: %v (must be positive)", time.Duration(d))
}

func (d NegativeDuration) ValidDurationRange() (min, max time.Duration) {
    if d >= 0 {
        panic(fmt.Sprintf("ev3dev: invalid negative duration: %v", d))
    }
    return 0, MaxInt64
}

[kortschak]

Use of fmt.Errorf in:

• led.go
• buttons.go
• ev3dev.go
• lego_port.go
• sensor.go
• speaker.go