Golang : Function wrapper that takes arguments and return result example
Continuing from our previous "primitive" tutorial on implementing a simple metaprogramming by creating a wrapper for a function. In this tutorial, we will explore how to define a wrapper function that takes in arguments and how to return a result.
This code example shows how to write a wrapper function the takes in an argument and influence the log level output.
package main
import (
"fmt"
"github.com/sirupsen/logrus"
"time"
)
var log = logrus.New()
type toBeWrapped func()
func LogTimeTaken(function toBeWrapped, level int) {
// 0 for debug, 1 for Info, 2 for Warn, 3 for Error, 4 for Fatal, 5 for Panic
if level == 0 {
log.Level = logrus.DebugLevel
} else if level == 1 {
log.Level = logrus.InfoLevel
} else if level == 2 {
log.Level = logrus.WarnLevel
} else if level == 3 {
log.Level = logrus.ErrorLevel
} else if level == 4 {
log.Level = logrus.FatalLevel
} else if level == 5 {
log.Level = logrus.PanicLevel
}
startTime := time.Now()
function()
endTime := time.Now()
log.Info("Time taken is about ----->> ", endTime.Sub(startTime))
log.Warn("TOO SLOW!")
if level >= 3 {
log.Error("No INFO and WARNING this time. Log level is set to Error. Abort!")
}
}
func main() {
HWfunc := func() {
fmt.Println("\n\n\nHello World \n\n\n")
}
// set to debug level, will not abort, will display both INFO and WARNING
LogTimeTaken(HWfunc, 0)
// set to warning level, STILL WILL not abort.
// will not display INFO because WARN level is higher than INFO
LogTimeTaken(HWfunc, 2)
// set to ErrorLevel
LogTimeTaken(HWfunc, 3)
}
Output:
Hello World
INFO[0000] Time taken is about ----->> 32.551µs
WARN[0000] TOO SLOW!
Hello World
WARN[0000] TOO SLOW!
Hello World
ERRO[0000] No INFO and WARNING this time. Log level is set to Error. Abort!
As you can see, the output behavior is controlled by the log level that we set in the second argument of the LogTimeTaken()
function.
And now let's learn how to return a string
value from the wrapped function, we simply change the type from
type toBeWrapped func()
to
type toBeWrapped func() string
We will use string
type for this tutorial, you are welcome to change to int
or any type you prefer. Run this code below to see how a wrapped function can return a string value.
package main
import (
"fmt"
)
// we expect the wrapped function to return string type
// change to suitable type for your own use or use interface for returning dynamic value
type toBeWrapped func() string
func WrappedFunctionThatReturnSomething(function toBeWrapped) string { // added string type for return
response := function() // wrapped function return value will be stored in response variable
return response // and return to outer function - the wrapper function
}
func main() {
WrappedFunction := func() string { // added string type for return
return "Hello World from a wrapped(inner) function"
}
returned := WrappedFunctionThatReturnSomething(WrappedFunction)
fmt.Println("The wrapped function says : ", returned)
}
Output:
The wrapped function says : Hello World from a wrapped(inner) function
Happy coding!
References:
https://socketloop.com/tutorials/golang-metaprogramming-example-of-wrapping-a-function
See also : Golang : How to save log messages to file?
By Adam Ng
IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.
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