What does it mean to have a variable that is only valid within the handler

Question content

In the go-optical documentation they say:

as a rule of thumb, you must only use context values within the
handler, and you must not keep any references

Is it ok if I pass the context as a function argument like this:

func getlist(c *fiber.ctx) error {
   result, err := user.search(c)
}

func search(c *fiber.ctx) (user, err) {
   id := c.params("id")
}

Is this considered a bad practice?

I don’t quite understand this sentence:

as soon as you return from the handler, any values you have obtained
from the context will be re-used in future requests and will change
below your feet.

So, if I have sent the response to the client, will the value of params be reused? Reused by whom? By me or at someone else's request?

func getlist(c *fiber.ctx) error {
   id := c.params("id") // 911
   return c.sendstring("hello, world!")
}

If the value of id is 911, does it mean that other people's requests will also get 911?

What does it mean

will change below your feet

Can anyone explain it in detail to make it easier for a beginner like me to understand? Thanks...

Correct answer

The actual context object can be reused by the framework after calling your handler, so you cannot rely on its state after returning from the handler .

Is it ok if I pass the context as a function parameter like this?

This is fine, as long as Search does not store the context elsewhere. If it just uses the value in the context to do the search and returns the results, that's fine.

So, if I have sent the response to the client, will the value of params be reused? Reused by whom? By me or at someone else's request?

The framework will reuse the actual context object while handling later requests.

What does "changes will happen under your feet" mean?

If you do not follow the above advice and instead keep a reference to the context after returning from the handler, the values ​​in that context will change unexpectedly because the framework is using the context for new requests.

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