add Custom Validator section to Validation docs

docs/basics/validation.md

@@ -227,3 +227,65 @@ Validators can also be combined to build complex validations using operators.
 |`!`|prefix|Inverts a validator, requiring the opposite.|
 |`&&`|infix|Combines two validators, requires both.|
 |`||`|infix|Combines two validators, requires one.|
+
+
+
+## Custom Validator
+
+
+
+To create a custom validator for validating a zip code, Here is the steps:
+
+First let's create a struct to for `ZipCode` validator.
+
+```swift
+extension ValidatorResults {
+ /// `ValidatorResult` of a validator that validates whether a `String` is a valid zip code.
+ public struct ZipCode {
+ /// The input is a valid zip code
+ public let isValidZipCode: Bool
+ }
+}
+```
+Next, comform the `ZipCode` to `ValidatorResult`
+
+```swift
+extension ValidatorResults.ZipCode: ValidatorResult {
+ public var isFailure: Bool {
+ !self.isValidZipCode
+ }
+
+ public var successDescription: String? {
+ "is a valid zip code"
+ }
+
+ public var failureDescription: String? {
+ "is not a valid zip code"
+ }
+}
+```
+Finally let's write the validation logic
+```swift
+private let zipCodeRegex: String = "^\\d{5}(?:[-\\s]\\d{4})?$"
+
+extension Validator where T == String {
+ /// Validates whether a `String` is a valid zip code.
+ public static var zipCode: Validator<T> {
+ .init {
+ guard
+ let range = $0.range(of: zipCodeRegex, options: [.regularExpression]),
+ range.lowerBound == $0.startIndex && range.upperBound == $0.endIndex
+ else {
+ return ValidatorResults.ZipCode(isValidZipCode: false)
+ }
+ return ValidatorResults.ZipCode(isValidZipCode: true)
+ }
+ }
+}
+```
+
+Now we can use it
+
+```swift
+validations.add("zipCode", as: ZipCode.self, is: .zipCode, required: true)
+```