chapter 08 finished;

 chapter 09 initialized

learning_go/08_errors/Makefile

@@ -0,0 +1,21 @@
+.DEFAULT_GOAL := run
+
+fmt:
+	go fmt ./...
+.PHONY: fmt
+
+lint: fmt
+	golint ./...
+.PHONY: lint
+
+vet: fmt
+	go vet ./...
+.PHONY: vet
+
+build: vet
+	go build panic_recover_example.go
+.PHONY: build
+
+run: vet
+	go run panic_recover_example.go
+.PHONY: run

learning_go/08_errors/README.md

@@ -12,3 +12,16 @@
 #### Sentinel errors
 * should be treated as `read-only` values
 * shouldn't be modified or created
+
+#### Errors are values
+* `error` is an interface
+* thus, you can implement your own error
+* for interface to be equal to `nil` (`== nil`), both base type and value should be `nil`
+* most common way is to return `nil` as error's value if no error occurred
+
+#### Wrapping errors
+* sequence of errors, wrapped is called `error chain`
+* `errors.Is` and `errors.As` are used to work with error chains
+
+#### Panic and recover
+* shouldn't be overused

learning_go/08_errors/errors_is_example.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+func fileChecker(name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return fmt.Errorf("in fileChecker: %w", err)
+	}
+	f.Close()
+	return nil
+}
+
+func bckp_main() {
+	err := fileChecker("not_here.txt")
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			fmt.Println("That file doesn't exist")
+		}
+	}
+}

learning_go/08_errors/go.mod

@@ -0,0 +1,3 @@
+module main
+
+go 1.20

learning_go/08_errors/panic_example.go

@@ -0,0 +1,11 @@
+package main
+
+import "os"
+
+func doPanic(msg string) {
+	panic(msg)
+}
+
+func bis_bckp_main() {
+	doPanic(os.Args[0])
+}

learning_go/08_errors/panic_recover_example.go

@@ -0,0 +1,16 @@
+package main
+
+func div60(i int) {
+	defer func() {
+		if v := recover(); v != nil {
+			println("recovered:", v)
+		}
+	}()
+	println(60 / i)
+}
+
+func main() {
+	for _, val := range []int{1, 2, 0, 3} {
+		div60(val)
+	}
+}

learning_go/09_modules_packages_imports/README.md

@@ -0,0 +1,18 @@
+# 09_modules_packages_imports
+
+### Intro
+* repositories
+* modules
+* packages
+* 1 or more packages per module
+* 1 module per 1 repository
+
+### Modules
+* `go.mod` file is necessary (and needs to be correct of course)
+* `go.mod` file contains:
+    - module name
+    - go version
+    - dependencies
+    - version of dependencies
+    - (optional) replace 
+    - (optional) exclude

learning_go/README.md

@@ -9,7 +9,7 @@ Directory for studying 'experiment', learning from papercover book "Język Go. T
 - [x] chapter 05 - functions
 - [x] chapter 06 - pointers
 - [x] chapter 07 - types, methods and interfaces
-- [ ] chapter 08 - errors
+- [x] chapter 08 - errors
 - [ ] chapter 09 - modules, packages and imports
 - [ ] chapter 10 - concurrency in Go
 - [ ] chapter 11 - standard library