Validation Types

All validation rules are members of FormValidator.Type<T>, a sealed class.

Required

Fails when the value is blank or null.

ValidationField(value = username.value, name = "Username", type = FormValidator.Type.Required) {
    username = username.copy(error = it)
}

Email

Checks that the value matches a valid email address format.

ValidationField(value = email.value, name = "Email", type = FormValidator.Type.Email) {
    email = email.copy(error = it)
}

MustBeMoreThan

Fails when a numeric value is not greater than min.

ValidationField(
    value = age.value,
    name = "Age",
    type = FormValidator.Type.MustBeMoreThan(min = 18)
) { age = age.copy(error = it) }

MustBeLessThan

Fails when a numeric value is not less than max.

ValidationField(
    value = discount.value,
    name = "Discount",
    type = FormValidator.Type.MustBeLessThan(max = 100)
) { discount = discount.copy(error = it) }

MustBeInRange

Fails when a numeric value falls outside [min, max].

ValidationField(
    value = quantity.value,
    name = "Quantity",
    type = FormValidator.Type.MustBeInRange(min = 1, max = 99)
) { quantity = quantity.copy(error = it) }

MustBeEqualTo

Fails when the value does not equal target. Useful for confirm-password fields.

ValidationField(
    value = confirmPassword.value,
    name = "Confirm Password",
    type = FormValidator.Type.MustBeEqualTo(target = password.value)
) { confirmPassword = confirmPassword.copy(error = it) }

Custom

Provide your own predicate. Return null to pass, or an error message string to fail.

ValidationField(
    value = username.value,
    name = "Username",
    type = FormValidator.Type.Custom { value ->
        if (value.length < 3) "Username must be at least 3 characters" else null
    }
) { username = username.copy(error = it) }

Optional

Skips validation entirely — the field is always considered valid. Use for fields that should participate in Flow.Down ordering without blocking submission.

ValidationField(
    value = bio.value,
    name = "Bio",
    type = FormValidator.Type.Optional
) { bio = bio.copy(error = it) }

Validation flow

FormValidator.Flow controls which fields are checked and in what order:

Flow	Behaviour
`Down`	Top-to-bottom; stops at the first failing field
`Up`	Bottom-to-top; stops at the first failing field
`Splash`	All fields validated simultaneously

FormValidator(flow = FormValidator.Flow.Splash, fields = ...)