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Enhance CoroutineDispatcher.invoke with contract #4554

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Enhance CoroutineDispatcher.invoke with contract #4554

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17 changes: 16 additions & 1 deletion kotlinx-coroutines-core/common/src/Builders.common.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -177,10 +177,25 @@ public suspend fun <T> withContext(
* completes, and returns the result.
*
* This inline function calls [withContext].
*
* Example usage:
* ```
* Dispatchers.IO { someFile.exists() } // Checking the file system is blocking I/O.
* ```
*
* The code above is a shorthand to `withContext(Dispatchers.IO) { someFile.exists() }`,
* with the added safety that **only the dispatcher** can be replaced, i.e. it's not possible
* to do `randomCoroutineContext { someFile.exists() }` as it would be possible using
* `withContext`, so it's not possible to unintendedly break structured concurrency with this operator.
*/
public suspend inline operator fun <T> CoroutineDispatcher.invoke(
noinline block: suspend CoroutineScope.() -> T
): T = withContext(this, block)
): T {
contract {
callsInPlace(block, InvocationKind.EXACTLY_ONCE)
}
return withContext(this, block)
}

// --------------- implementation ---------------

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