在smlnj中，如何转换“字符串选项" “串"? [英] in smlnj how do you convert "string option" to "string"?

问题描述

请帮助我不知道字符串选项的作用.

Please help I have no idea how what a string option does.

是否可以将字符串选项转换为字符串?

is it possible to convert string option to a string?

推荐答案

如前所述，您可以使用模式匹配来获得所需的结果. 所以，像这样:

As already pointed out you could use pattern matching to get the desired result. So, something like this:

fun foo(NONE) = ""
  | foo(SOME a) = a;

但是您可以避免麻烦，并使用 SML库中的Option.valOf 函数，而不是仅仅这样做:

But you could spare the trouble and use Option.valOf function from SML library instead by just doing:

Option.valOf(SOME "my string");(或者只是newacct在注释中指出的valOf(SOME "my string");.)

Option.valOf(SOME "my string"); (Or just valOf(SOME "my string"); as newacct pointed out in the comments.)

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