Issue Description:

```
import Foundation

struct DBUser: Encodable {
static var name: String { return "user" }
var name: String
}

let u = DBUser(name: "foo")
let data = try! JSONEncoder().encode(u)
print(String(data: data, encoding: .utf8)!)
```

Expected output is `{"name":"foo"}`, but it outputs

```
$ swift test.swift
{"name":"user"}
```