【kotlin】inline function 原碼分析

@kotlin.internal.InlineOnly

表示這個函式是一個內聯函式，但它只能在 Kotlin 標準函式庫內部使用。這個註解通常用於指示編譯器只將這個函式內聯化，而不生成實際的函式調用。

inline fun <T, R> T.let(block: (T) -> R): R 函式定義：

• inline fun：這表示 let 函式是一個內聯函式，其函式體會被內聯到每一個函式調用處。
• <T, R>：這是泛型參數列表。T 表示函式調用的對象的類型，而 R 表示 block 函式的返回類型。
• T.let(block: (T) -> R)：這是函式的簽名。它擁有一個 block 參數，這個 block 是一個接受 T 類型參數並返回 R 類型的函數。
• : R：函式的返回類型是 R，即 block 函式的返回值類型。

inline fun <T> T.apply(block: T.() -> Unit): T 函式定義：

• inline fun：這表示 apply 函式是一個內聯函式，其函式體會被內聯到每一個函式調用處。
• <T>：這是一個泛型參數，表示函式可以操作任意類型 T 的對象。
• T.apply(block: T.() -> Unit)：這是函式的簽名。它接受一個名為 block 的參數，這個 block 是一個以 T 類型的接收者（receiver）為上下文的函數型參數，沒有任何輸入，並且沒有返回值 (Unit)。
• : T：函式的返回類型是 T，也就是函式調用的對象本身。

/**
 * Calls the specified function [block] and returns its result.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#run).
 */
@kotlin.internal.InlineOnly
public inline fun <R> run(block: () -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    return block()
}

/**
 * Calls the specified function [block] with `this` value as its receiver and returns its result.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#run).
 */
@kotlin.internal.InlineOnly
public inline fun <T, R> T.run(block: T.() -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    return block()
}

/**
 * Calls the specified function [block] with the given [receiver] as its receiver and returns its result.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#with).
 */
@kotlin.internal.InlineOnly
public inline fun <T, R> with(receiver: T, block: T.() -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    return receiver.block()
}

/**
 * Calls the specified function [block] with `this` value as its receiver and returns `this` value.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#apply).
 */
@kotlin.internal.InlineOnly
public inline fun <T> T.apply(block: T.() -> Unit): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    block()
    return this
}

/**
 * Calls the specified function [block] with `this` value as its argument and returns `this` value.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#also).
 */
@kotlin.internal.InlineOnly
@SinceKotlin("1.1")
public inline fun <T> T.also(block: (T) -> Unit): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    block(this)
    return this
}

/**
 * Calls the specified function [block] with `this` value as its argument and returns its result.
 *
 * For detailed usage information see the documentation for [scope functions](https://kotlinlang.org/docs/reference/scope-functions.html#let).
 */
@kotlin.internal.InlineOnly
public inline fun <T, R> T.let(block: (T) -> R): R {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }
    return block(this)
}