Go Defer Eldad Marciano Software Engineer @Red Hat 

Agenda ● Defer Scope ● Defer Order ● Using defer with direct vs pointers 

What it’s all about “defers the execution of a function until the surrounding function returns.” 

What it’s all about “Defers the execution of a function until the surrounding function returns.” Crosspond to the finally Java or Python. 

What it’s all about “defers the execution of a function until the surrounding function returns.” Crosspond to the finally Java or Python. “finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling” 

Python finally scope 

Go defer in function scope 

What is all about “defers the execution of a function until the surrounding function returns.” Crosspond to the finally Java or Python. “finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling” The tricky part?! 

Thumb rules Defer belongs to func and not to a block. 

Thumb rules Defer belongs to func and not to a block. 

Thumb rules Defer belongs to func and not to a block. 

Thumb rules Defer belongs to func and not to a block. Remember that Defer stacked the defer calls. “When a function returns, its deferred calls are executed in LIFO”. 

Defer Stack LIFO 

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Thumb rules Defer belongs to func and not to a block. Remember that Defer stacked the defer calls. “When a function returns, its deferred calls are executed in LIFO”. Be Careful when use defer inside infinite loop. 

Defer in a infinite loop 

Use infinite loop with pre-defined func 

Use infinite loop with pre-defined func 

Use infinite loop with pre-defined func 

Use infinite loop with pre-defined func 

Defer in a infinite loop - risks Problems Memory leak Too many files descriptors. Defer will never happen 

Thumb rules Defer belongs to func and not to a block. Remember that Defer stacked the defer calls. “When a function returns, its deferred calls are executed in LIFO”. Be Careful when use defer inside infinite loop. Defer order, be Careful with sleeps or periodical functions 

Python finally 

Go Defer 

Defer gotchas 

Links Credits to Inanc Gumus 1. 5 Gotchas of Defer in Go   —   Part I 2. Go Defer Simplified with Practical Visuals 

Q & A