Nate/continue default initialization (apple#193)

* Use type inference for flags / options

* Use default value syntax for arg/option arrays

* Allow a default for flag arrays

* Fix some whitespace

* Allow arguments validations to warn instead of fail

* Move nonsense flag warning to argument validation

* Update guides/readme with default literal syntax

Documentation/01 Getting Started.md

@@ -133,7 +133,7 @@ struct Count: ParsableCommand {
     var outputFile: String
 
     @Flag()
-    var verbose: Bool
+    var verbose = false
 
     mutating func run() throws {
         if verbose {
@@ -175,7 +175,7 @@ struct Count: ParsableCommand {
     var outputFile: String
 
     @Flag(name: .shortAndLong)
-    var verbose: Bool
+    var verbose = false
 
     mutating func run() throws { ... }
 }
@@ -209,7 +209,7 @@ struct Count: ParsableCommand {
     var outputFile: String
 
     @Flag(name: .shortAndLong, help: "Print status updates while counting.")
-    var verbose: Bool
+    var verbose = false
 
     mutating func run() throws { ... }
 }
@@ -244,7 +244,7 @@ struct Count: ParsableCommand {
     var outputFile: String
 
     @Flag(name: .shortAndLong, help: "Print status updates while counting.")
-    var verbose: Bool
+    var verbose = false
 
     mutating func run() throws {
         if verbose {

Documentation/02 Arguments, Options, and Flags.md

@@ -26,24 +26,24 @@ The three preceding examples could be calls of this `Example` command:
 
 ```swift
 struct Example: ParsableCommand {
-    @Argument() var files: [String]
+    @Argument() var files: [String] = []
 
     @Option() var count: Int?
 
-    @Option var index: Int = 0
+    @Option() var index = 0
 
-    @Flag() var verbose: Bool
+    @Flag() var verbose = false
 
-    @Flag() var stripWhitespace: Bool
+    @Flag() var stripWhitespace = false
 }
 ```
 
 This example shows how `ArgumentParser` provides defaults that speed up your initial development process:
 
 - Option and flag names are derived from the names of your command's properties.
-- Whether arguments are required and what kinds of inputs are valid is based on your properties' types.
+- What kinds of inputs are valid, and whether arguments are required, is based on your properties' types and default values.
 
-In this example, all of the properties have default values — Boolean flags always default to `false`, optional properties default to `nil`, and arrays default to an empty array. An option, flag, or argument with a `default` parameter can also be omitted by the user.
+In this example, all of the properties have default values (optional properties default to `nil`).
 
 Users must provide values for all properties with no implicit or specified default. For example, this command would require one integer argument and a string with the key `--user-name`.
 
@@ -70,12 +70,12 @@ Usage: example --user-name <user-name> <value>
   See 'example --help' for more information.
 ```
 
-When using the `default` parameter for an array property, the default values will not be included if additional values are passed on the command line.
+When providing a default value for an array property, any user-supplied values replace the entire default.
 
-```
+```swift
 struct Lucky: ParsableCommand {
-  @Argument(default: [7, 14, 21])
-  var numbers: [Int]
+  @Argument()
+  var numbers = [7, 14, 21]
 
   mutating func run() throws {
     print("""
@@ -104,10 +104,10 @@ You can override this default by specifying one or more name specifications in t
 ```swift
 struct Example: ParsableCommand {
     @Flag(name: .long)  // Same as the default
-    var stripWhitespace: Bool
+    var stripWhitespace = false
 
     @Flag(name: .short)
-    var verbose: Bool
+    var verbose = false
 
     @Option(name: .customLong("count"))
     var iterationCount: Int
@@ -214,7 +214,7 @@ Flags are most frequently used for `Bool` properties. You can generate a `true`/
 ```swift
 struct Example: ParsableCommand {
     @Flag(inversion: .prefixedNo)
-    var index: Bool = true
+    var index = true
 
     @Flag(inversion: .prefixedEnableDisable)
     var requiredElement: Bool
@@ -225,7 +225,7 @@ struct Example: ParsableCommand {
 }
 ```
 
-When providing a flag inversion, you can pass your own default with normal property initialization syntax (`@Flag var foo: Bool = true`). If you want to require that the user specify one of the two inversions, use a non-Optional type and do not pass a default value.
+When declaring a flag with an inversion, set the default by specifying `true` or `false` as the property's initial value. If you want to require that the user specify one of the two inversions, leave off the default value.
 
 In the `Example` command defined above, a flag is required for the `requiredElement` property. The specified prefixes are prepended to the long names for the flags:
 
@@ -241,19 +241,19 @@ Error: Missing one of: '--enable-required-element', '--disable-required-element'
 To create a flag with custom names for a Boolean value, to provide an exclusive choice between more than two names, or for collecting multiple values from a set of defined choices, define an enumeration that conforms to the `EnumerableFlag` protocol.
 
 ```swift
-enum CacheMethod: EnumerableFlag {
+enum CacheMethod: String, EnumerableFlag {
     case inMemoryCache
     case persistentCache
 }
 
-enum Color: EnumerableFlag {
+enum Color: String, EnumerableFlag {
     case pink, purple, silver
 }
 
 struct Example: ParsableCommand {
     @Flag() var cacheMethod: CacheMethod
 
-    @Flag() var colors: [Color]
+    @Flag() var colors: [Color] = []
 
     mutating func run() throws {
         print(cacheMethod)
@@ -302,7 +302,7 @@ For example, this command defines a `--verbose` flag, a `--name` option, and an
 
 ```swift
 struct Example: ParsableCommand {
-    @Flag() var verbose: Bool
+    @Flag() var verbose = false
     @Option() var name: String
     @Argument() var file: String?
 
@@ -349,8 +349,8 @@ The default strategy for parsing options as arrays is to read each value from a
 
 ```swift
 struct Example: ParsableCommand {
-    @Option() var file: [String]
-    @Flag() var verbose: Bool
+    @Option() var file: [String] = []
+    @Flag() var verbose = false
 
     mutating func run() throws {
         print("Verbose: \(verbose), files: \(file)")
@@ -400,8 +400,8 @@ The default strategy for parsing arrays of positional arguments is to ignore  al
 
 ```swift
 struct Example: ParsableCommand {
-    @Flag() var verbose: Bool
-    @Argument() var files: [String]
+    @Flag() var verbose = false
+    @Argument() var files: [String] = []
 
     mutating func run() throws {
         print("Verbose: \(verbose), files: \(files)")

Documentation/03 Commands and Subcommands.md

@@ -56,7 +56,7 @@ In this case, the `Options` type accepts a `--hexadecimal-output` flag and expec
 ```swift
 struct Options: ParsableArguments {
     @Flag(name: [.long, .customShort("x")], help: "Use hexadecimal notation for the result.")
-    var hexadecimalOutput: Bool
+    var hexadecimalOutput = false
 
     @Argument(help: "A group of integers to operate on.")
     var values: [Int]
@@ -124,7 +124,7 @@ extension Math.Statistics {
         var kind: Kind = .mean
 
         @Argument(help: "A group of floating-point values to operate on.")
-        var values: [Double]
+        var values: [Double] = []
 
         func calculateMean() -> Double { ... }
         func calculateMedian() -> Double { ... }
@@ -151,7 +151,7 @@ extension Math.Statistics {
             abstract: "Print the standard deviation of the values.")
 
         @Argument(help: "A group of floating-point values to operate on.")
-        var values: [Double]
+        var values: [Double] = []
 
         mutating func run() {
             if values.isEmpty {

Documentation/04 Customizing Help.md

@@ -7,10 +7,10 @@ You can provide help text when declaring any `@Argument`, `@Option`, or `@Flag`
 ```swift
 struct Example: ParsableCommand {
     @Flag(help: "Display extra information while processing.")
-    var verbose: Bool
+    var verbose = false
 
     @Option(help: "The number of extra lines to show.")
-    var extraLines: Int = 0
+    var extraLines = 0
 
     @Argument(help: "The input file.")
     var inputFile: String?
@@ -42,12 +42,12 @@ Here's the same command with some extra customization:
 ```swift
 struct Example: ParsableCommand {
     @Flag(help: "Display extra information while processing.")
-    var verbose: Bool
+    var verbose = false
 
     @Option(help: ArgumentHelp(
         "The number of extra lines to show.",
         valueName: "n"))
-    var extraLines: Int = 0
+    var extraLines = 0
 
     @Argument(help: ArgumentHelp(
         "The input file.",

Documentation/05 Validation and Errors.md

@@ -16,7 +16,7 @@ struct Select: ParsableCommand {
     var count: Int = 1
 
     @Argument()
-    var elements: [String]
+    var elements: [String] = []
 
     mutating func validate() throws {
         guard count >= 1 else {
@@ -127,12 +127,11 @@ struct ExampleDataModel: Codable {
 }
 
 struct Example: ParsableCommand {
-
   // Reads in the argument string and attempts to transform it to
   // an `ExampleDataModel` object using the `JSONDecoder`. If the
   // string is not valid JSON, `decode` will throw an error and
   // parsing will halt.
-  @Argument(transform: ExampleDataModel.dataModel )
+  @Argument(transform: ExampleDataModel.dataModel)
   var inputJSON: ExampleDataModel
 
   // Specifiying this option will always cause the parser to exit

Documentation/06 Manual Parsing and Testing.md

@@ -12,11 +12,11 @@ Let's implement the `Select` command discussed in [Validation and Errors](05%20V
 
 ```swift
 struct SelectOptions: ParsableArguments {
-    @Option
+    @Option()
     var count: Int = 1
 
     @Argument()
-    var elements: [String]
+    var elements: [String] = []
 }
 ```
 

Examples/math/main.swift

@@ -35,11 +35,11 @@ struct Math: ParsableCommand {
 struct Options: ParsableArguments {
     @Flag(name: [.customLong("hex-output"), .customShort("x")],
           help: "Use hexadecimal notation for the result.")
-    var hexadecimalOutput: Bool = false
+    var hexadecimalOutput = false
 
     @Argument(
         help: "A group of integers to operate on.")
-    var values: [Int]
+    var values: [Int] = []
 }
 
 extension Math {
@@ -103,7 +103,7 @@ extension Math.Statistics {
         var kind: Kind = .mean
 
         @Argument(help: "A group of floating-point values to operate on.")
-        var values: [Double]
+        var values: [Double] = []
 
         func validate() throws {
             if (kind == .median || kind == .mode) && values.isEmpty {
@@ -166,7 +166,7 @@ extension Math.Statistics {
             abstract: "Print the standard deviation of the values.")
 
         @Argument(help: "A group of floating-point values to operate on.")
-        var values: [Double]
+        var values: [Double] = []
 
         mutating func run() {
             if values.isEmpty {
@@ -189,15 +189,15 @@ extension Math.Statistics {
             abstract: "Print the quantiles of the values (TBD).")
 
         @Argument(help: "A group of floating-point values to operate on.")
-        var values: [Double]
+        var values: [Double] = []
 
         // These args and the validation method are for testing exit codes:
         @Flag(help: .hidden)
-        var testSuccessExitCode: Bool = false
+        var testSuccessExitCode = false
         @Flag(help: .hidden)
-        var testFailureExitCode: Bool = false
+        var testFailureExitCode = false
         @Flag(help: .hidden)
-        var testValidationExitCode: Bool = false
+        var testValidationExitCode = false
         @Option(help: .hidden)
         var testCustomExitCode: Int32?
 

Examples/repeat/main.swift

@@ -16,7 +16,7 @@ struct Repeat: ParsableCommand {
     var count: Int?
 
     @Flag(help: "Include a counter with each repetition.")
-    var includeCounter: Bool = false
+    var includeCounter = false
 
     @Argument(help: "The phrase to repeat.")
     var phrase: String

Examples/roll/main.swift

@@ -13,19 +13,19 @@ import ArgumentParser
 
 struct RollOptions: ParsableArguments {
     @Option(help: ArgumentHelp("Rolls the dice <n> times.", valueName: "n"))
-    var times: Int = 1
+    var times = 1
 
     @Option(help: ArgumentHelp(
         "Rolls an <m>-sided dice.",
         discussion: "Use this option to override the default value of a six-sided die.",
         valueName: "m"))
-    var sides: Int = 6
+    var sides = 6
 
     @Option(help: "A seed to use for repeatable random generation.")
     var seed: Int?
 
     @Flag(name: .shortAndLong, help: "Show all roll results.")
-    var verbose: Bool = false
+    var verbose = false
 }
 
 // If you prefer writing in a "script" style, you can call `parseOrExit()` to

README.md

@@ -13,7 +13,7 @@ import ArgumentParser
 
 struct Repeat: ParsableCommand {
     @Flag(help: "Include a counter with each repetition.")
-    var includeCounter: Bool
+    var includeCounter = false
 
     @Option(name: .shortAndLong, help: "The number of times to repeat 'phrase'.")
     var count: Int?