The Rush Expression

Rush

The rush expression is used to run a block of two or more async expressions concurrently (simultaneously).

When the fastest subexpression completes, any expression that follows the rush is evaluated, and any remaining subexpressions continue to evaluate.



|  | set WinnerResult = rush: |
| --- | --- |
|  | # All three async functions start at the same time |
|  | AsyncFunctionLongTime() |
|  | AsyncFunctionShortTime()  # This will win and its result is used |
|  | AsyncFunctionMediumTime() |
|  | # Next expression is called after the fastest async function (AsyncFunctionShortTime()) completes. |
|  | # All other subexpression tasks (AsyncFunctionLongTime(), AsyncFunctionMediumTime()) continue. |
|  | NextExpression(WinnerResult) |
|  | AsyncFunction4() |
|  | # If any rush subexpression tasks are still running when AsyncFunction4 completes |
|  | # then they are now canceled. |

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The following code shows the syntax for the rush expression.



|  | expression0 |
| --- | --- |
|  | rush: |
|  | slow-expression |
|  | mid-expression |
|  | fast-expression |
|  | expression1 |

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The diagram below shows the execution flow for the expressions.

Visualization of the order the expressions in the rush block finish Diagram showing the execution flow of the rush expression

Rush Expression Use

Where you can use a `rush` expression	Async contexts
Invocation time of the `rush` expression	Async
Requirements for `rush` code block	The body of the `rush` expression must have at least two expressions, and all of the expressions must be async.
What the `rush` expression does	Is similar to `race`, but expressions that complete after first completion continue. If any expressions effectively complete at the same simulation update, then the earlier encountered expression that completes breaks any tie. Any incomplete expressions continue to evaluate until they complete, or until the enclosing async context completes, at which point, any remaining losing expressions are canceled — whichever occurs first.
When the `rush` expression completes	The `rush` expression completes when the first expression in the code block has completed. This could be the fastest, shortest length, first completed, or least amount of time to complete.
When the next expression after `rush` starts	Any next expression that follows the `rush` expression is started when the completed expression finishes.
Result of the `rush` expression	The result of a `rush` expression is the result of the first completed expression. The result type is the most common compatible type of all expressions in the code block.

A rush expression cannot currently be used in the body of an iteration expression like loop or for. If it must be used, then wrap it in an async function and have the iteration expression call that function.