Custom Known Value Checks

Custom known value checks can be created by implementing the knownvalue.Check interface.

type Check interface {
    CheckValue(value any) error
    String() string
}

For example, a StringContains implementation could look as follows:

var _ knownvalue.Check = stringContains{}

type stringContains struct {
    value string
}

func (v stringContains) CheckValue(other any) error {
    otherVal, ok := other.(string)

    if !ok {
        return fmt.Errorf("expected string value for StringContains check, got: %T", other)
    }

    if !strings.Contains(otherVal, v.value) {
        return fmt.Errorf("expected string %q to contain %q for StringContains check", otherVal, v.value)
    }

    return nil
}

func (v stringContains) String() string {
    return v.value
}

func StringContains(value string) stringContains {
    return stringContains{
        value: value,
    }
}

`CheckValue` Method Implementation

The other parameter passed to the CheckValue method is one of the following types:

bool
map[string]any
[]any
string

Note: Numerical values will be of type json.Number, with an underlying type of string.

Refer to the following built-in known value checks for implementations that handle the different types that can be passed to the CheckValue method in the other parameter:

Custom Known Value Checks

CheckValue Method Implementation

`CheckValue` Method Implementation