關於Smart KeyPath - Chiao-Te, Ni
===

{%hackmd FGRWt1UuTFKk0wSbGgg-SA %}

> 請從這裡開始

## Slide
{%speakerdeck chiaoteni/swift-smart-keypath %}

* 範例： let keyPath = \UIView.frame
* 延後取值的特性
* 也可以用在非NSObject
* KeyPath -> read only
* WritableKeyPath -> read/write (for variable)
* ReferenceWritableKeyPath -> read/write (for variable/constant, Class only)
* 系統會根據屬性(如frame 或是 width) 自動回傳不同的keyPath型別
* e.g. \UIView.frame.size -> ReferenceWritableKeyPath
* e.g. \UIView.frame.width -> KeyPath
* 實際應用範例：對array做extension 驗證物件得值是否符合預期

ticket.sorted(\.price, by: <)

## second case
hold check array

## Fluent autoLayout
coding syle: Fluent interface
### before

label.translatesAutoresizingMaskIntoConstraints = false
label.constraint(...).isactive = true

### after

label
.setAnchor(\.widthanchor, ..., to: view.widthanchor)
.setAnchor(\.heightanchor, ..., to: view.heightanchor)

Fluent Builder
`@dynamicMemberLookup`

//java
Type variableName = new Type.builder()
    .a() -> return builder
    .b() -> return builder
    .build() -> 這邊才把實體new出來

## conclusion

###### tags:`iPlayground2019`