for case let ... where

Swift ⟩ Pattern Matching ⟩ Sentence Patterns ⟩

• case: pattern matching.

• let: variable binding.

• where: condition on bound variable.

💈範例

💾 程式： Mirror.handleChildren()

⭐️ 注意： for case let ... where 加條件的方式跟 if/guard case let 不一樣❗️

// mirror of `subject`
let mirror = Mirror(reflecting: subject)

// ⭐ for case let ... where 
//   (pattern-match tuples + data binding + condition)
// ------------------------------------------------------
//            ↱ ⭐ child.label ignored     ╭── ⭐ where ───╮
for case let (_, value) in mirror.children where value is T {
    // ...
}

// ⭐ for case let ... where
for case let .loaded(data) in states where data.count > 2
{ ... }

⭐️ 重點

⭐️ 注意：下列程式碼雖然類似 for case let ... where，但完全沒有用到 pattern matching 的概念喔❗️

// for ... in ... where
for item in array where item.year > 2000 { … }

👥 相關

• Mirror.handleChildren() - use if case let ... where sentence pattern.