How Do Named Returns in Go Handle Panics Differently Than Normal Returns?

Why Can a Normal Return Hide a Panic That a Named Return Correctly Provides to the Caller?

In Go, the return statement initializes all result parameters to their zero values before executing deferred functions. If there are named result parameters and the return statement is not reached, these named parameters will retain the zero value.

This behavior is demonstrated in the example provided:

func NormalReturns(n int) error {
    var err error
    defer catch(&err)
    panicIf42(n)
    return err
}

Here, the err variable is initialized to nil, but since the return statement is not reached due to a panic, it remains nil. Even though the defer catch() modifies err, this change is not reflected in the returned value because the return statement specifies an empty expression list.

In contrast, named returns allow deferred functions to modify return values after the return statement and before returning to the caller. This is exemplified in the following function:

func NamedReturns(n int) (err error) {
    defer catch(&err)
    panicIf42(n)
    return
}

In this case, err is initialized to nil, but the deferred catch() is able to modify it before the function returns. As a result, any non-zero value assigned to err will be returned to the caller.

This behavior highlights the key difference between named and normal returns. With named returns, deferred functions can alter the return values, providing a way to ensure that relevant information is propagated back to the caller, even in the event of a panic.

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