What is the Swift equivalent of isEqualToString in Objective-C

Question

I am trying to run the code below   import UIKit  class LoginViewController  UIViewController     IBOutlet var username   UITextField   UITextField    IBOutlet var password   UITextField   UITextField     IBAction func loginButton sender   AnyObject         if username  isEqual        password isEqual                    println  Sign in failed  Empty character             My previous code was in Objective-C  which was working fine    if   self username text  isEqualToString                self password text  isEqualToString             I assume I cannot use isEqualToString in Swift  Any help would be appreciated

User · Answer

Actually  it feels like swift is trying to promote strings to be treated less like objects and more like values  However this doesn t mean under the hood swift doesn t treat strings as objects  as am sure you all noticed that you can still invoke methods on strings and use their properties    For example -    example of calling method  String to Int conversion  let intValue     12  toInt    println  This is a intValue now   intValue        example of using properties  fetching uppercase value of string  let caUpperValue    ca  uppercaseString println  This is the uppercase of ca   caUpperValue      In objectC you could pass the reference to a string object through a variable  on top of calling methods on it  which pretty much establishes the fact that strings are pure objects    Here is the catch when you try to look at String as objects  in swift you cannot pass a string object by reference through a variable  Swift will always pass a brand new copy of the string  Hence  strings are more commonly known as value types in swift  In fact  two string literals will not be identical        They are treated as two different copies   let curious     ca       ca   println  This will be false   and the answer is    curious      As you can see we are starting to break aways from the conventional way of thinking of strings as objects and treating them more like values  Hence  isEqualToString which was treated as an identity operator for string objects is no more a valid as you can never get two identical string objects in Swift  You can only compare its value  or in other words check for equality        let NotSoCuriousAnyMore     ca      ca    println  This will be true   and the answer is    NotSoCuriousAnyMore      This gets more interesting when you look at the mutability of string objects in swift  But thats for another question  another day  Something you should probably look into  cause its really interesting     Hope that clears up some confusion  Cheers

User · Answer

For the UITextField text comparison I am using below code and working fine for me  let me know if you find any error         if txtUsername text isEmpty    txtPassword text isEmpty          Do some stuff   else if txtUsername text            amp  amp  txtPassword text                    Do some stuff

User · Answer

With Swift you don t need anymore to check the equality with isEqualToString  You can now use     Example     let x    hello  let y    hello  let isEqual    x    y    now isEqual is true

User · Answer

In Swift  the    operator is equivalent to Objective C s isEqual  method  it calls the isEqual method instead of just comparing pointers  and there s a new     method for testing that the pointers are the same   so you can just write this as   if username          password             println  Sign in failed  Empty character

User · Answer

Use    operator instead of isEqual  Comparing Strings  Swift provides three ways to compare String values  string equality  prefix equality  and suffix equality   String Equality  Two String values are considered equal if they contain exactly the same characters in the same order   let quotation    We re a lot alike  you and I   let sameQuotation    We re a lot alike  you and I   if quotation    sameQuotation       println  These two strings are considered equal        prints  These two strings are considered equal          For more read official documentation of Swift  search Comparing Strings

User · Answer

In Swift the isEmpty function it will check if the string is empty    if username isEmpty    password isEmpty         println  Sign in failed  Empty character

User · Answer

I addition to  JJSaccolo answer  you can create custom equals method as new String extension like   extension String        func isEqualToString find  String  - gt  Bool           return String format  self     find           And usage   let a    abc  let b    abc   if a isEqualToString b         println  Equals       For sure original operator    might be better  works like in Javascript  but for me isEqual method gives some code clearness that we compare Strings  Hope it will help to someone

User · Answer

One important point is that Swift s    on strings might not be equivalent to Objective-C s -isEqualToString   The peculiarity lies in differences in how strings are represented between Swift and Objective-C  Just look on this example  let composed    quot    quot     U 00D6 LATIN CAPITAL LETTER O WITH DIAERESIS let decomposed   composed decomposedStringWithCanonicalMapping     U 004F LATIN CAPITAL LETTER O     U 0308 COMBINING DIAERESIS   composed utf16 count    1 decomposed utf16 count    2  let composedNSString   composed as NSString let decomposedNSString   decomposed as NSString  decomposed    composed    true  Strings are equal decomposedNSString    composedNSString    false  NSStrings are not  NSString s are represented as a sequence of UTF   16 code units  roughly read as an array of UTF-16  fixed-width  code units   Whereas Swift Strings are conceptually sequences of  quot Characters quot   where  quot Character quot  is something that abstracts extended grapheme cluster  read Character   any amount of Unicode code points  usually something that the user sees as a character and text input cursor jumps around   The next thing to mention is Unicode  There is a lot to write about it  but here we are interested in something called  quot canonical equivalence quot   Using Unicode code points  visually the same  quot character quot  can be encoded in more than one way  For example   quot    quot  can be represented as a precomposed  quot    quot  or as decomposed A        that s why in example composed utf16 and decomposed utf16 had different lengths   A good thing to read on that is this great article  - NSString isEqualToString    according to the documentation  compares NSStrings code unit by code unit  so           A        Swift s String    compares characters by canonical equivalence                 A          In swift the above example will return true for Strings  That s why - NSString isEqualToString   is not equivalent to Swift s String     Equivalent pure Swift comparison could be done by comparing String s UTF-16 Views  decomposed utf16 elementsEqual composed utf16     false  UTF-16 code units are not the same decomposedNSString    composedNSString    false  UTF-16 code units are not the same decomposedNSString isEqual to  composedNSString as String     false  UTF-16 code units are not the same  Also  there is a difference between NSString    NSString and String    String in Swift  The NSString    will cause isEqual and UTF-16 code unit by code unit comparison  where as String    will use canonical equivalence  decomposed    composed    true  Strings are equal decomposed as NSString    composed as NSString    false  UTF-16 code units are not the same  And the whole example  let composed    quot    quot     U 00D6 LATIN CAPITAL LETTER O WITH DIAERESIS let decomposed   composed decomposedStringWithCanonicalMapping     U 004F LATIN CAPITAL LETTER O     U 0308 COMBINING DIAERESIS   composed utf16 count    1 decomposed utf16 count    2  let composedNSString   composed as NSString let decomposedNSString   decomposed as NSString  decomposed    composed    true  Strings are equal decomposedNSString    composedNSString    false  NSStrings are not  decomposed utf16 elementsEqual composed utf16     false  UTF-16 code units are not the same decomposedNSString    composedNSString    false  UTF-16 code units are not the same decomposedNSString isEqual to  composedNSString as String     false  UTF-16 code units are not the same

[string] What is the Swift equivalent of isEqualToString in Objective-C?

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