什么时候应该使用let {}，什么时候只是简单的！= null

Question

你会怎样用更多kotlinic的方式编写下面的代码？

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 

我可以用让，但我觉得它使代码更复杂，难以理解

Answer 1

• 常见共享代码 - 在这种情况下，错误报告和失败结果返回 - 可合并为local function。
• 导致返回的可空性（在这种情况下，s3data可为空）通常可以用返回的?: elvis operator代替。
• 当反复输入相同的变量（在这种情况下，访问s3data）时，run块是适当的。如果混淆，请参阅What is a "receiver" in Kotlin?
• 正如另一个答案中所述，如果/ else块是Kotlin中的表达式。

因此我会发现下面的实现最ideomatic，受本地函数的参数恰当的命名：

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()}") 
    } 
} 

你的问题是在代码审查接壤，所以你可能也很高兴知道有一个dedicated Stack Exchange network just for that.然而，之前读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 
}