How can I handle erroneous return values from deferred functions in Go?

Handling Deferred Functions with Erroneous Return Values in Go

gometalinter and errcheck rightfully raise a warning when a function that returns a variable is deferred without checking its returned error. This can lead to unhandled errors and potential runtime issues.

The idiom to handle this scenario is not to defer the function itself, but rather to wrap it in another function that checks the returned value. Here's an example:

<code class="go">defer func() {
    if err := r.Body.Close(); err != nil {
        // Handle the error
    }
}()</code>

By using an anonymous function, you can capture the return value of the deferred function and handle any errors that occur.

Alternatively, you can create a helper function to simplify the process:

<code class="go">func Check(f func() error) {
    if err := f(); err != nil {
        // Handle the error
    }
}</code>

This helper function can then be used to defer multiple functions, ensuring that their return values are checked:

<code class="go">defer Check(r.Body.Close)
defer Check(SomeOtherFunc)</code>

You can even extend the helper function to accept multiple functions:

<code class="go">func Checks(fs ...func() error) {
    for i := len(fs) - 1; i >= 0; i-- {
        if err := fs[i](); err != nil {
            // Handle the error
        }
    }
}</code>

This allows you to defer multiple functions and handle their errors in a more concise and organized manner:

<code class="go">defer Checks(r.Body.Close, SomeOtherFunc)</code>

To ensure that the errors are handled in the correct order, the Checks() function uses a downward loop to execute the functions in reverse order of their declaration. This aligns with the execution order of deferred functions, where the last deferred function is executed first.

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