Open Radar

 
Summary:
There are many instances where I find myself creating structs that are simply configuration objects for an API (such as `attributes` for `NSAttributedString`). Since only a subset of the configurations provided by the object need to be customized or provided at any one time, I generally write an `init` that takes all of the properties, but provides default values. This allows the user to only configure what they care about, i.e.:

```
struct Options {
	let foo: String?
	let bar: Bool
	let baz: Int

	init(foo: String? = nil, bar: Bool = true, baz: Int = 0) {
		self.foo = foo
		self.bar = bar
		self.baz = baz
	}
}

let options = Options(bar: false)
```

While I find this to be an incredibly powerful tool, there’s a whole lot of boiler plate going on, and `Options` only has 3 properties. It would be amazing if Swift could generate this init for me by inferring the default values in the initializer from the default values of the properties itself.

Steps to Reproduce:
Attempt to compile the following:

```
struct Options {
	let foo: String? = nil
	let bar: Bool = true
	let baz: Int = 0
}

let options = Options(bar: false)
```

Expected Results:
This compiles, because the generated initializer can take `bar` and `bad` as optional parameters with default values.

Actual Results:
This does not compile, because the generated initializer is simply `Foo()`

Regression:
N/A

Notes:
N/A