Why Does `defer recover()` Fail to Catch Panics, While `defer func() { recover() }()` Succeeds?

Why defer recover() Not Catch Panics?

The Question:

Why does a call to defer func() { recover() }() successfully recover a panicking goroutine, but a call to defer recover() not?

The Answer:

As per the documentation of recover(), "If recover is called outside the deferred function, it will not stop a panicking sequence."

In the case of defer recover(), recover() itself is the deferred function. Therefore, it does not call itself, leading to a continued panicking sequence.

If recover() were to call itself as the deferred function, it would stop the panicking sequence. However, this would be illogical.

An Interesting Variant:

The following code also avoids a panic:

package main

func main() {
    var recover = func() { recover() }
    defer recover()
    panic("panic")
}

Here, we create a recover variable with a function value that calls the built-in recover() function. By deferring the call to this variable's value, we invoke the built-in recover(), which then stops the panicing sequence.

The above is the detailed content of Why Does `defer recover()` Fail to Catch Panics, While `defer func() { recover() }()` Succeeds?. For more information, please follow other related articles on the PHP Chinese website!