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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
/// Protocol for Generated Structs to conform to
/// Dictionary maps field names to internal IDs and uses Reflection
/// to iterate through all fields.
/// `writeFieldValue(_:name:type:id:)` calls `TSerializable.write(to:)` internally
/// giving a nice recursive behavior for nested TStructs, TLists, TMaps, and TSets
public protocol TStruct : TSerializable {
static var fieldIds: [String: Int32] { get }
static var structName: String { get }
}
public extension TStruct {
static var fieldIds: [String: (id: Int32, type: TType)] { return [:] }
static var thriftType: TType { return .struct }
func write(to proto: TProtocol) throws {
// Write struct name first
try proto.writeStructBegin(name: Self.structName)
try self.forEach { name, value, id in
// Write to protocol
try proto.writeFieldValue(value, name: name,
type: value.thriftType, id: id)
}
try proto.writeFieldStop()
try proto.writeStructEnd()
}
/// Provides a block for handling each (available) thrift property using reflection
/// Caveat: Skips over optional values
/// Provides a block for handling each (available) thrift property using reflection
///
/// - parameter block: block for handling property
///
/// - throws: rethrows any Error thrown in block
private func forEach(_ block: (_ name: String, _ value: TSerializable, _ id: Int32) throws -> Void) rethrows {
// Mirror the object, getting (name: String?, value: Any) for every property
let mirror = Mirror(reflecting: self)
// Iterate through all children, ignore empty property names
for (propName, propValue) in mirror.children {
guard let propName = propName else { continue }
if let tval = unwrap(any: propValue, parent: mirror) as? TSerializable, let id = Self.fieldIds[propName] {
try block(propName, tval, id)
}
}
}
/// Any can mysteriously be an Optional<Any> at the same time,
/// this checks and always returns Optional<Any> without double wrapping
/// we then try to bind value as TSerializable to ignore any extension properties
/// and the like and verify the property exists and grab the Thrift
/// property ID at the same time
///
/// - parameter any: Any instance to attempt to unwrap
///
/// - returns: Unwrapped Any as Optional<Any>
private func unwrap(any: Any, parent: Mirror) -> Any? {
let mi = Mirror(reflecting: any)
if parent.displayStyle != .enum && mi.displayStyle != .optional { return any }
if mi.children.count == 0 { return nil }
let (_, some) = mi.children.first!
return some
}
}
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