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I am studying swift.

I don't understand the code written on the following site.

https://qiita.com/H_Crane/items/e784a5f7c4fb5e6470e6

In the [Japanese judgment] item

NSPredicate (format: "SELF MATCHES% @", range) .evaluate (with: self)

I read the official reference of NSPredicate, but I couldn't understand the contents.
In particular, I don't understand the meaning of the argument"SELF MATCHES% @" ;.

Thank you.

Official Reference NSPredicate
https://developer.apple.com/documentation/foundation/nspredicate

  • Answer # 1

    Cited sites

    [Swift] Validation String Extension collection using iOS default functions

    A little code excerpt from
    extension String {
        /// "Kanji" or not
        var isKanji: Bool {
            let range = "^ [\ u {3005} \ u {3007} \ u {303b} \ u {3400}-\ u {9fff} \ u {f900}-\ u {faff} \ u {20000}-\ u {2ffff}] + $"
            return NSPredicate (format: "SELF MATCHES% @", range) .evaluate (with: self)
        }

    What does "SELF MATCHES% @"" mean?

    First SELF is from Literals,

      

    SELF
      Represents the object being evaluated.

    In other words, the object to be evaluated, in this case self of evaluate (with: self).
    Since this code is a String extension, self is a String.

    MATCHES from String Comparisons

      

    MATCHES
      The left hand expression equals the right hand expression using a regex-style comparison according to ICU v3 (for more details see the ICU User Guide for Regular Expressions).

    Since it is

    , it checks whether SELF (target character string) on ​​the left side satisfies the regular expression on the right side.

    The right side is% @, but as in Parser Basics,

      

    The format string supports printf-style format specifiers such as% x (see Formatting String Objects). Two important format specifiers are% @ and% K.

      

    % @ is a var arg substitution for an object value—often a string, number, or date.

    Performs parameter expansion like the printf function.

    NSPredicate (format: "SELF MATCHES% @", range)

    So% @ is range,

      

    "^ [\ u {3005} \ u {3007} \ u {303b} \ u {3400}-\ u {9fff} \ u {f900}-\ u {faff} \ u {20000}- \ u {2ffff}] + $"

    .

    This is a regular expression.

    In the end, we are checking whether the target string satisfies the above regular expression.

  • Answer # 2

      

    I don't understand the meaning of the argument "quote SELF MATCHES% @"".

    SELF(Since String is passed, String itself) is% @(arrangement range is assigned) andMATCHES(match ) Or not.

    From Japanese documentation

      The

    MATCHES operator uses the ICU regular expression package, as shown in the following example:

    Because it is

    , it means whether the regular expression represented byrangematches self (String itself).