Branch in Verse | Fortnite Documentation | Epic Developer Community

A branch expression starts a block of one or more async subexpressions, and any expression that follows after is executed immediately, without waiting for the branch expressions to complete.

You can use branch essentially to treat any async block of code as though it were fire-and-forget immediate, but it still must be called within an async context.

Verse

branch:
    # This block continues until completed
    AsyncFunction1()    # Starts effectively the same time as AsyncFunction3()
    Method1()  # Block can be mixed with immediate expressions
    AsyncFunction2()
AsyncFunction3()  # Starts effectively the same time as AsyncFunction1()
# If branch block task is still running when AsyncFunction3 completes
# then any remaining branch task is canceled

branch:
    # This block continues until completed
    AsyncFunction1()    # Starts effectively the same time as AsyncFunction3()
    Method1()  # Block can be mixed with immediate expressions
    AsyncFunction2()
AsyncFunction3()  # Starts effectively the same time as AsyncFunction1()
# If branch block task is still running when AsyncFunction3 completes
# then any remaining branch task is canceled

The following code shows the syntax for the branch expression.

Verse

expression0
branch:
    slow-expression
    mid-expression
    fast-expression
expression1

expression0
branch:
    slow-expression
    mid-expression
    fast-expression
expression1

The diagram below shows the execution flow of the expressions.

Diagram showing the execution flow of the branch expression

It is similar to the unstructured concurrency spawn expression, but branch allows for any arbitrary block of code, and is only permissible within, and bounded by, an enclosing async context. Because of this, branch is preferred over spawn whenever possible.

Branch Expression Use


Where you can use a `branch` expression	Async contexts
Invocation time of the `branch` expression	Immediate
Requirements for `branch` code block	The `branch` expression must have at least one async expression.
What the `branch` expression does	The body of the `branch` expression is started as soon as it is encountered. The body of the branch expression continues to evaluate until the code block completes or the enclosing async context completes — whichever occurs first — at which point the `branch` code block task is canceled.
When the `branch` expression completes	The `branch` expression completes immediately.
When the next expression after `branch` starts	Any expression that follows the `branch` expression is started immediately.
Result of the `branch` expression	A `branch` expression has no result, so its result type is `void`.

A branch expression may not currently be used in the body of an iteration expression such as loop or for. If it must be used then wrap it in an async function and have the iteration expression call that function.

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Branch Expression Use