← All notes

Answer: In Go, defer schedules a function call to run when the surrounding function returns, which makes cleanup like closing files easy. panic stops normal execution and unwinds the stack, running deferred calls; recover, called inside a deferred function, stops a panic and lets the program continue.

Three rules of defer

1. A deferred call's arguments are evaluated when the defer statement runs, not when the call happens.
2. Deferred calls run in last-in, first-out order after the function returns.
3. Deferred functions can read and set the function's named return values.

f, err := os.Open(name)
if err != nil { return err }
defer f.Close()

panic and recover

defer func() {
    if r := recover(); r != nil {
        log.Println("recovered:", r)
    }
}()

recover only has an effect inside a deferred function during a panic; otherwise it returns nil.

Claims

• id: C1 claim: A deferred function's arguments are evaluated when defer is evaluated. source: S1 evidence: "A deferred function’s arguments are evaluated when the defer statement is evaluated."
• id: C2 claim: Deferred calls execute in Last In First Out order. source: S1 evidence: "Deferred function calls are executed in Last In First Out order after the surrounding function"
• id: C3 claim: Deferred functions may assign named return values. source: S1 evidence: "Deferred functions may read and assign to the returning function’s named return values."
• id: C4 claim: Defer is commonly used to simplify clean-up. source: S1 evidence: "Defer is commonly used to simplify functions that perform various clean-up actions."
• id: C5 claim: Effective Go says deferred functions execute in LIFO order. source: S2 evidence: "Deferred functions are executed in LIFO order, so this code will cause"

Sources

• [S1] Defer, Panic, and Recover - The Go Programming Language. The Go Authors (go.dev). https://go.dev/blog/defer-panic-and-recover . License: CC BY 4.0 (go.dev text). Accessed 2026-11-04.
• [S2] Effective Go - The Go Programming Language. The Go Authors (go.dev). https://go.dev/doc/effective_go . License: CC BY 4.0 (go.dev text). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_e7ddbcp1,
  author = {{iinventedlight}},
  title = {{Go defer, panic and recover}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/go-defer-panic-recover/},
  note = {Permanent ID iil:note:e7ddbcp1. License: CC-BY-4.0.},
}

Markdown

Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.

For language models and agents: start at /llms.txt. This page in Markdown: /library/notes/go-defer-panic-recover.md.