What Is the Backslash(\) Used for in Swiftui

What is the backslash(\) used for in SwiftUI?

\.self it's a identity keypath that apple added for:

Add the ability to reference the identity key path, which refers to the entire input value it is applied to.

More info in proposal.

What does backslash do in Swift?

The backslash has a few different meanings in Swift, depending on the context. In your case, it means string interpolation:

print("The total cost of my meal is \(dictionary["pizza"]! + dictionary["ice cream"]!)")

...is the same as:

print("The total cost of my meal is " + String(dictionary["pizza"]! + dictionary["ice cream"]!))

But the first form is more readable. Another example:

print("Hello \(person.firstName). You are \(person.age) years old")

Which may print something like Hello John. You are 42 years old. Much clearer than:

print("Hello " + person.firstName + ". You are " + String(person.age) + " years old")

(Swift) how to print \ character in a string?

For that and also future reference:

\0 – Null character (that is a zero after the slash)
\\ – Backslash itself.  Since the backslash is used to escape other characters, it needs a special escape to actually print itself.
\t  – Horizontal tab
\n – Line Feed
\r  – Carriage Return
\”  – Double quote.  Since the quotes denote a String literal, this is necessary if you actually want to print one.
\’  – Single Quote.  Similar reason to above.

Swift - remove single backslash

You can just replace those backslashes, for example:

let string2 = string1.stringByReplacingOccurrencesOfString("\\", withString: "")

Or, to avoid the confusion over the fact that the backslash within a normal string literal is escaped with yet another backslash, we can use an extended string delimiter of #" and "#:

let string2 = string1.stringByReplacingOccurrencesOfString(#"\"#, withString: "")

But, if possible, you really should fix that API that is returning those backslashes, as that's obviously incorrect. The author of that code was apparently under the mistaken impression that forward slashes must be escaped, but this is not true.

Bottom line, the API should be fixed to not insert these backslashes, but until that's remedied, you can use the above to remove any backslashes that may occur.

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In the discussion in the comments below, there seems to be enormous confusion about backslashes in strings. So, let's step back for a second and discuss "string literals". As the documentation says, a string literal is:

You can include predefined String values within your code as string literals. A string literal is a fixed sequence of textual characters surrounded by a pair of double quotes ("").

Note, a string literal is just a representation of a particular fixed sequence of characters in your code. But, this should not be confused with the underlying String object itself. The key difference between a string literal and the underlying String object is that a string literal allows one to use a backslash as an "escape" character, used when representing special characters (or doing string interpolation). As the documentation says:

String literals can include the following special characters:

• The escaped special characters \0 (null character), \\ (backslash), \t (horizontal tab), \n (line feed), \r (carriage return), \" (double quote) and \' (single quote)
• An arbitrary Unicode scalar, written as \u{n}, where n is a 1–8 digit hexadecimal number with a value equal to a valid Unicode code point

So, you are correct that in a string literal, as the excerpt you quoted above points out, you cannot have an unescaped backslash. Thus, whenever you want to represent a single backslash in a string literal, you represent that with a \\.

Thus the above stringByReplacingOccurrencesOfString means "look through the string1, find all occurrences of a single backslash, and replace them with an empty string (i.e. remove the backslash)."

Consider:

let string1 = "foo\\bar"

print(string1)                    // this will print "foo\bar"
print(string1.characters.count)   // this will print "7", not "8"

let string2 = string1.stringByReplacingOccurrencesOfString("\\", withString: "")

print(string2)                    // this will print "foobar"
print(string2.characters.count)   // this will print "6"

A little confusingly, if you look at string1 in the "Variables" view of the "Debug" panel or within playground, it will show a string literal representation (i.e. backslashes will appear as "\\"). But don't be confused. When you see \\ in the string literal, there is actually only a single backslash within the actual string. But if you print the value or look at the actual characters, there is only a single backslash in the string, itself.

In short, do not conflate the escaping of the backslash within a string literal (for example, the parameters to stringByReplacingOccurrencesOfString) and the single backslash that exists in the underlying string.

identified(by: \.self) - what does it do?

1. Looks like common is a static variable that they created to help their demo. It's just an extension on ContentSizeCategory. Something like this:

extension ContentSizeCategory {
     static var common = [ContentSizeCategory.accessibilityLarge,
                          ContentSizeCategory.accessibilityMedium,
                        ContentSizeCategory.extraSmall]

}

2. ContentSizeCategory is an enum, conforms to Hashable that means every type is uniquely identifiable. Below is the signature of identified function, when it is called you need to tell what's the key path that it should use in order to uniquely identify items. So \.self is basically telling the whole self is unique because it conforms to Hashable.

func identified<ID>(by getID: KeyPath<Binding<Value.Element>, ID>) -> IdentifierValuePairs<Binding<Value>, ID> where ID : Hashable

Swift: What does backslash dot \. mean?

tl;dr: We take a look at the Swift language reference, and sure enough, the usage of this backslash-dot notation is called a key-path-expression.

(The question has been sufficiently answered, by this point.)

A more hands-on approach on how to get to that piece of buried documentation:

As you can see from the code you posted, the User class contains a property named email.

Notice that, assuming you're using Xcode, if you replace return \.email with return \, you get the compile-error "Expected expression path in Swift key path", so this is a hint that this backslash-dot notation might have to do with something called a key path.

From that documentation on key-path, we see that we could also have written \User.email (and you can try it out in Xcode with no compiler error).

Understanding the greater context of what's going on in that code:

So, semantically, to understand the meaning of the usernameKey declaration you're looking at, we might want to understand what a WritableKeyPath is. In simple, from the documentation, we see that a WritableKeyPath is: "A key path that supports reading from and writing to the resulting value."

So, we see that the usernameKey declaration takes in a WritableKeyPath object and returns a String that is User.email.

Furthermore, it's apparent that the User class needs this usernameKey property in order to conform to the PasswordAuthenticatable protocol, which was imported on the first line with import Authentication (if you care to explore there, take a look at Dependencies > Auth 2.0.0 > Authentication > Basic > BasicAuthenticatable.swift).

Swift - Remove character from string

Swift uses backslash to escape double quotes. Here is the list of escaped special characters in Swift:

• \0 (null character)
• \\ (backslash)
• \t (horizontal tab)
• \n (line feed)
• \r (carriage return)
• \" (double quote)
• \' (single quote)

This should work:

text2 = text2.replacingOccurrences(of: "\\", with: "", options: NSString.CompareOptions.literal, range: nil)

Why my SwiftUI component has a circle-backslash?

This is because you can't use ScrollView in Widgets (you're not allowed to scroll anyway).

Widget views are static and they don't allow much interaction (with the exception of Link).

You need to replace the ScrollView with another container, eg. a HStack.

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