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https://github.com/Pungyeon/clean-go-article.git
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commit
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23
README.md
23
README.md
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@ -311,7 +311,7 @@ func getReference(extension string) (string, bool) {
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if !ok {
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return EmptyItem, false
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}
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return refIface.(string)
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return refIface.(string), true
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}
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func getItemByReference(reference string) (Item, error) {
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@ -503,6 +503,7 @@ func getVal(num int) (string, error) {
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if val == "" {
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return NewValue() // pretend function
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}
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return val, err
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}
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func main() {
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@ -813,27 +814,27 @@ There are other scenarios in which it is common to find `nil` values that can ca
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```go
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type App struct {
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Cache *KVCache
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Cache *KVCache
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}
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type KVCache struct {
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mtx sync.RWMutex
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store map[string]string
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store map[string]string
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}
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func (cache *KVCache) Add(key, value string) {
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cache.mtx.Lock()
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defer cache.mtx.Unlock()
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cache.store[key] = value
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cache.store[key] = value
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}
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```
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This code is absolutely fine. However, the danger is that our `App` can be initialised incorrectly, without initialising the `Cache` property within. Should the following code be invoked, our application will panic:
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```go
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app := App{}
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app.Cache.Add("panic", "now")
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app := App{}
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app.Cache.Add("panic", "now")
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```
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The `Cache` property has never been initialised and is therefore a `nil` pointer. Thus, invoking the `Add` method like we did here will cause a panic, with the following message:
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@ -844,14 +845,14 @@ Instead, we can turn the `Cache` property of our `App` structure into a private
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```go
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type App struct {
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cache *KVCache
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cache *KVCache
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}
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func (app *App) Cache() *KVCache {
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if app.cache == nil {
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app.cache = NewKVCache()
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}
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return app.cache
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if app.cache == nil {
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app.cache = NewKVCache()
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}
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return app.cache
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}
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```
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