什麼時候應該使用let {}，什麼時候只是簡單的！= null

Question

你會怎樣用更多kotlinic的方式編寫下面的代碼？

var returnValue = ... 
val s3data = presignedUrl.body() 
if (s3data != null) { 
    val uploadImage = api.uploadImage(s3data.bucketUrl, s3data.awsAccessKeyId, s3data.policy, s3data.key, s3data.signature, body).execute() 
    if (!uploadImage.isSuccessful) { 
     crashReporterService.sendIssue("Failed uploading file", "Failed uploading file ${uploadImage.raw()}") 
     returnValue = Result.FAILURE 
    } else { 
     returnValue = Result.SUCCESS 
    } 
} else { 
    crashReporterService.sendIssue("Failed uploading image", "Error - ${presignedUrl.raw()}") 
    returnValue = Result.FAILURE 
} 

return returnValue 

我可以用讓，但我覺得它使代碼更復雜，難以理解

Answer 1

• 常見共享代碼 - 在這種情況下，錯誤報告和失敗結果返回 - 可合併爲local function。
• 導致返回的可空性（在這種情況下，s3data可爲空）通常可以用返回的?: elvis operator代替。
• 當反覆輸入相同的變量（在這種情況下，訪問s3data）時，run塊是適當的。如果混淆，請參閱What is a "receiver" in Kotlin?
• 正如另一個答案中所述，如果/ else塊是Kotlin中的表達式。

因此我會發現下面的實現最ideomatic，受本地函數的參數恰當的命名：

fun foo() { 
    fun failure(p0: String, p1: String) = crashReporterService.sendIssue(p0, p1).let { Result.FAILURE } 
    val s3data = presignedUrl.body() ?: return failure("Failed uploading image", "Error - ${presignedUrl.raw()}") 
    val uploadImage = s3data.run { api.uploadImage(bucketUrl, awsAccessKeyId, policy, key, signature, body).execute() } 

    return if (uploadImage.isSuccessful) { 
     Result.SUCCESS 
    } else { 
     failure("Failed uploading file", "Failed uploading file ${uploadImage.raw()}") 
    } 
} 

你的問題是在代碼審查接壤，所以你可能也很高興知道有一個dedicated Stack Exchange network just for that.然而，之前讀A guide to Code Review for Stack Overflow users。

Answer 2

if/else is an expression in Kotlin，所以下面肯定更是Kotlinesque：

val s3data = presignedUrl.body() 
return if (s3data != null) { 
    val uploadImage = api.uploadImage(s3data.bucketUrl, s3data.awsAccessKeyId, s3data.policy, s3data.key, s3data.signature, body).execute() 
    if (!uploadImage.isSuccessful) { 
     crashReporterService.sendIssue("Failed uploading file", "Failed uploading file ${uploadImage.raw()}") 
     Result.FAILURE 
    } else { 
     Result.SUCCESS 
    } 
} else { 
    crashReporterService.sendIssue("Failed uploading image", "Error - ${presignedUrl.raw()}") 
    Result.FAILURE 
}