error-handling - 用户输入为空时应该抛出什么异常？

Question

我一直在搜索一段时间，但我肯定已经错过了，是否有任何文档说明当值不正确/为空时应该抛出什么？

例如，Python具有 ValueError ，并且文档中明确说明了何时使用它。

我有以下方法:

proc getJobinfo {question} {
    puts -nonewline "$question: "
    flush stdout
    gets stdin answer
    set cleanedanswer [string trim [string totitle $answer]]
    if {$cleanedanswer eq ""} {
       # What error should be thrown?
    }
    return $cleanedanswer
}

我已经搜索了 throw ， error 和 catch ，但是找不到它。

Answer 1

Tcl没有预定义的异常层次结构。 throw命令带有2个参数:type是单词列表； message是人类的错误消息。

你可以做类似的事情

proc getJobinfo {question} {
    ...
    if {$cleanedanswer eq ""} {
        throw {Value Empty} "Please provide a suitable answer."
    } elseif {[string length $cleanedanswer] < 5} {
        throw {Value Invalid} "Your answer is too short."
    } else ...
    return $cleanedanswer
}

如果要捕获该错误:

try {
    set answer [getJobinfo "What is the answer to this question"]
} trap {Value *} msg {
    puts "Value Error: $msg"
}

throw和 try通过 type调用的 throw字进行交互。我们抛出“空值”或“无效值”。在陷阱中，我们完全匹配 Value，但不会完全匹配 *。事后看来， *不应该存在。
初次阅读时， try 联机帮助页并不十分清晰:

trap pattern variableList script

This clause matches if the evaluation of body resulted in an error and the prefix of the -errorcode from the interpreter's status dictionary is equal to the pattern. The number of prefix words taken from the -errorcode is equal to the list-length of pattern, and inter-word spaces are normalized in both the -errorcode and pattern before comparison.

模式不是 regexp或 string match意义上的模式:它是一个单词列表，该单词列表与try正文中抛出的单词列表一一对应。
try可以用多个陷阱实现以具有级联的“陷阱”:

try {
    set answer [getJobinfo "What is the answer to this question"]

} trap {Value Empty} msg {
    do something specific here

} trap {Value Invalid} msg {
    do something specific here

} trap {Value} msg {
    do something general for some other "throw {Value anything} msg"

} on error e {
    this can be default catch-all for any other error

} finally {
    any cleanup code goes here
}