Pass function as argument in Go

Question

I've tried to create a function in Go that used to retry any fail query functions (usually because serialization issue).

func retryer(functionA func(interface{}) (interface{}, []error), maxRetry int, waitBetween time.Duration) interface{} { //when no error in functionA, retryer returns whatever functionA returns //when maxRetry is reached, returns nil }

The functions I want to retry are looked like this

func GetTopStudent(classId string) ([]Student, []error) { //queries top 10 students for class with classId } func GetAverageStudentScores(classId string, from time.Time, until time.Time) ([]Pair, []error) { //queries all average score using aggregate, grouping by studentId //Pair behaves like C++ pair<string,string> }

But, the results is a compile error

cannot use GetTopStudent (type func(string) ([]Student, []error)) as type func(interface{}) (interface {}, []error) in argument to retryer

I've tried to modify it a little and I got another compile error

cannot use GetTopStudent (type func(string) ([]Student, []error)) as type func(string) (interface {}, []error) in argument to retryer

Can anyone help me creating a general function to wrap a function to retry on error?

The signatures of the functions passed as a parameter must match the signature of the function type of the parameter exactly. You'll have to rewrite the functions you pass to take interface{}'s, and cast them to the appropriate types inside those functions. — xunatai
– xunatai, Commented Jun 14, 2017 at 4:13
That way, for N functions, I need N wrappers. I need the general function wrapper to greatly simplify me code. — Kuzunoha
– Kuzunoha, Commented Jun 14, 2017 at 4:25

abhink · Accepted Answer · 2017-06-14 05:19:11Z

A better way to solve your problem would be to use closures.

For example, change the type of retryer:

func retryer(f func() error, maxRetry int, waitBetween time.Duration) error { // retry and wait logic err := f() // error handling, retry, and wait logic return err }

Now call functions to be retried as:

// ... classId := "some value" // ... var st []Student var errors []error err := retryer(func() error { st, errors = GetTopStudent(classId) // handle errors return nil }, numTries, waitTime) // use st here

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