Try/Catch/Finally in Go

Experiment in Golang that tries to bring the exception behaviour of Java/Python/C++ to Golang using the same syntax.

Experiment only!!

I as a Go developer, do not recomend to use this library in production or real world code. The Go language was designed to do not use expections, instead use the explicit error management suggested in Effective Go. A good programmer MUST write idiomatic code.

Instead you should use this project as a learning tool to understand the exceptions flow in a language like python/c++ and python.

It also shows that Go, even without explicit exceptions has the semantics needed to provide it exactly in the same way Java/C++ and Python does.

Approach

1. We need Try, Catch and Finally methods.
2. We need a Throw() method for rethrowing exceptions.
3. It needs to be stateless so it could be nested and used across many threads.

API examples:

1. Simple panic() inside Try

Unfortunately we have to include a Finally before a Catch. I have tried to find a way to avoid it, but looks impossible. Anyway, the behaviour and order of call is exactly the same than Java or Python.

import (
	"fmt"
	"github.com/manucorporat/try"
)

func main() {
	try.This(func() {
		panic("my panic")

	}).Finally(func() {
		fmt.Println("this must be printed after the catch")

	}).Catch(func(e try.E) {
		// Print crash
		fmt.Println(e)
	})
}

2. Finally is optional

import (
	"fmt"
	"github.com/manucorporat/try"
)

func main() {
	var obj interface{}
	obj = 2
	try.This(func() {
		// this operation will panic because obj is an integer
		text := obj.(string)
		fmt.Println(text)

	}).Catch(func(e try.E) {
		// Print crash
		fmt.Println(e)
	})
}

3. Rethrowing

import (
	"fmt"
	"github.com/manucorporat/try"
)

func main() {
	try.This(func() {
		panic("my panic")

	}).Finally(func() {
		fmt.Println("this must be printed after the catch")

	}).Catch(func(_ try.E) {
		fmt.Println("exception catched") // print
		try.Throw()                      // rethrow current exception!!
	})
}

4. Nested

package main

import (
	"fmt"
	"github.com/manucorporat/try"
)

func main() {
	try.This(func() {
		try.This(func() {
			panic("my panic")

		}).Catch(func(e try.E) {
			fmt.Println("fixing stuff") // print
			try.Throw()                 // rethrow current exception!!
		})

	}).Catch(func(e try.E) {
		// print
		fmt.Println(e)
	})
	fmt.Println("hey")
}

prints

fixing stuff
my panic
hey

Full covered with unit tests

• See test_try.go

Different cases of try/catch/finally

This Go package has the same behaviour than the implementation of exceptions in Java, C++ and Python.

1. No crash at all

try {
	print "1"
} catch(err) {
	print "2"
	print err
} finally {
	print "3"
}
print "4"

prints

1
3
4

2. Throw in try

try {
	print "1"
	throw "exception 1"
} catch(err) {
	print "2"
	print err
} finally {
	print "3"
}
print "4"

prints

1
2
exception 1
3
4

3. Throw in try and catch

try {
	print "1"
	throw "exception 1"
} catch(err) {
	print "2"
	throw "exception 2"
} finally {
	print "3"
}
print "4"

prints

1
2
3
---> uncatched exception 2

4. Throw in try, catch and finally

try {
	print "1"
	throw "exception 1"
} catch(err) {
	print "2"
	throw "exception 2"
} finally {
	print "3"
	throw "exception 3"
}
print "4"

prints

1
2
3
---> uncatched exception 3

yes! "exception 2" was throwed but "overwritten" by "exception 3"

5. finally is optional

try {
	print "1"
	throw "exception 1"
} catch(err) {
	print "2"
	throw "exception 2"
}
print "4"

prints

1
2
---> uncatched exception 2

5. Rethrowing exceptions

try {
	print "1"
	throw "exception 1"
} catch() {
	print "2"
	throw
}
print "4"

prints

1
2
---> uncatched exception 1