Built in Rules

Built-in Rules

All built-in rules accept an optional reason parameter. When omitted, a sensible default message is used. Supply your own wherever a more precise explanation adds value:

verify(user::age).atLeast(18, reason = "User must be at least 18 years old")

---

String rules

Applied to Verification<String>.

Rule	Fails when	Violation type
notBlank()	The string is blank	NotBlankViolation
minLength(min)	The string is shorter than min characters	MinLengthViolation
maxLength(max)	The string is longer than max characters	MaxLengthViolation
exactLength(length)	The string length does not equal length	ExactLengthViolation
lengthRange(min, max)	The string length is outside the range [min, max]	LengthRangeViolation

validateCollecting {
    verify(user::username).notBlank().minLength(3).maxLength(20)
    verify(user::bio).maxLength(160)
    verify(user::countryCode).exactLength(2)
}

---

Comparable rules

Applied to Verification<T> where T : Comparable<T>.

Rule	Fails when	Violation type
atLeast(min)	The value is less than min (inclusive)	AtLeastViolation
atMost(max)	The value is greater than max (inclusive)	AtMostViolation
between(min, max)	The value is outside the range [min, max]	BetweenViolation
greaterThan(min)	The value is not greater than min (exclusive)	GreaterThanViolation
lessThan(max)	The value is not less than max (exclusive)	LessThanViolation

validateCollecting {
    verify(order::total).greaterThan(0.0)
    verify(product::rating).between(1, 5)
    verify(user::age).atLeast(18)
}

---

Collection rules

Applied to Verification<C> where C : Collection<*>.

Rule	Fails when	Violation type
minSize(min)	The collection has fewer than min elements	MinSizeViolation
maxSize(max)	The collection has more than max elements	MaxSizeViolation
exactSize(size)	The collection size does not equal size	ExactSizeViolation
sizeRange(min, max)	The collection size is outside the range [min, max]	SizeRangeViolation
distinct()	The collection contains duplicate elements	DistinctViolation

validateCollecting {
    verify(order::items).minSize(1).maxSize(100)
    verify(user::tags).distinct().maxSize(10)
}

---

Equality rules

Applied to Verification<T>.

Rule	Fails when	Violation type
notNull()	The value is null	NotNullViolation
equalTo(expected)	The value does not equal expected	EqualToViolation
notEqualTo(forbidden)	The value equals forbidden	NotEqualToViolation
oneOf(allowed)	The value is not in allowed	OneOfViolation
noneOf(forbidden)	The value is in forbidden	NoneOfViolation

validateCollecting {
    verify(user::role).oneOf(setOf("admin", "editor", "viewer"))
    verify(user::status).notEqualTo("banned")
    verify(user::referralCode).notNull()
}

---

Violation types

Every built-in rule produces a typed violation that implements PathAwareViolation. In addition to reason, each violation carries the validationPath that identifies where in the validated structure the failure occurred.

All violation types are in the io.github.kverify.violations package.

Violation type	Carries
NotBlankViolation	validationPath, reason
MinLengthViolation	minLengthAllowed, actualLength, validationPath, reason
MaxLengthViolation	maxLengthAllowed, actualLength, validationPath, reason
ExactLengthViolation	expectedLength, actualLength, validationPath, reason
LengthRangeViolation	minLengthAllowed, maxLengthAllowed, actualLength, validationPath, reason
AtLeastViolation	minAllowed, actual, validationPath, reason
AtMostViolation	maxAllowed, actual, validationPath, reason
BetweenViolation	min, max, actual, validationPath, reason
GreaterThanViolation	minExclusive, actual, validationPath, reason
LessThanViolation	maxExclusive, actual, validationPath, reason
MinSizeViolation	minSizeAllowed, actualSize, validationPath, reason
MaxSizeViolation	maxSizeAllowed, actualSize, validationPath, reason
ExactSizeViolation	expectedSize, actualSize, validationPath, reason
SizeRangeViolation	minSizeAllowed, maxSizeAllowed, actualSize, validationPath, reason
DistinctViolation	actualSize, distinctSize, validationPath, reason
NotNullViolation	validationPath, reason
EqualToViolation	expected, actual, validationPath, reason
NotEqualToViolation	forbidden, validationPath, reason
OneOfViolation	allowed, actual, validationPath, reason
NoneOfViolation	forbidden, actual, validationPath, reason

These types let you handle specific failures by type rather than by parsing strings:

result.violations
    .filterIsInstance<MinLengthViolation>()
    .forEach { println("${it.validationPath}: must be at least ${it.minLengthAllowed} characters") }

Next steps

• Violation — understand the typed violations produced by these rules
• Verification — learn how rules are chained and applied