scala while loop assignment

As an example, here is a line with two expressions that would work better as a block: The only value we really care about keeping is amount, so lets combine the expressions including the x value into a block. So how do else if blocks still work correctly in Scala? Here is a short example demonstrating a three-deep nested expression block: These examples may not indicate compelling reasons to use expression blocks on their own. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. A statement is just an expression that doesnt return a value. In this version the Boolean expression is handled first, and then the result is matched to either true or false: The logic works out to the same as in the if .. else block but is implemented differently. Lets try it out by creating a for-loop that iterates over the sequence we built and printing each message, this time all on the same line instead of on their own lines. // getClassAsString is a method that takes a single argument of any type. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Is there an apt --force-overwrite option? Unlike them, only zero or one patterns can match; there is no fall-through from one pattern to the next one in line, nor is there a break statement that would prevent this fall-through. there was no do keyword: Scala 3 still supports the Scala 2 syntax for the sake of compatibility. The message 32 elided in the preceding example indicates that the errors stack trace (a list of all the nested function calls down to the one that caused the error) was reduced for readability. The resulting value is assigned to max, which we and the Scala compiler know will be an Int because both expressions have return values of type Int. The following is a syntax for while loop. Future chapters will continue this trend of defining concepts and structures in terms of expressions. Expressions provide a foundation for functional programming because they make it possible to return data instead of modifying existing data (such as a variable). This one is reporting that res10 has the type IndexedSeq[String], an indexed sequence of String, and is assigned a Vector, one of the implementations of IndexedSeq. Get full access to Learning Scala and 60K+ other titles, with free 10-day trial of O'Reilly. Why is the US residential model untouchable and unquestionable? But that's okay because you can put a code block anywhere. A do..while loop is used when we want the loop to run at least one time. The error type, scala.MatchError, indicates that this is a failure of the match expression to handle its input. Its similar to Java, but its syntax is consistent with match expressions: Scala also has a while loop construct. Come write articles for us and get featured, Learn and code with the best industry experts. Writing code in comment? Can't start Eclipse - Java was started but returned exit code=13, Identifying a novel about floating islands, dragons, airships and a mysterious machine. This is one of the main goals and benefits of functional programming. These are referred to as guards. Logically this is exactly the same as an if .. else if .. else block, and as a matter of syntax Scala recognizes the second if else as a nested expression of the outer if .. else block. Scala provides the different types of loops but in this article we understand while and do-while loops. Scala officially supports having multiple expressions follow the arrow (=>), but this is not recommended because it may reduce readability. Scala has a match expression, which in its most basic use is like a Java switch statement: However, match really is an expression, meaning that it returns a result based on the pattern match, which you can bind to a variable: match isnt limited to working with just integer values, it can be used with any data type: In fact, a match expression can be used to test a variable against many different types of patterns. Making statements based on opinion; back them up with references or personal experience. Pattern variables, if matched, may convert the input value to a value with a different type. As you read through the book, you will pick up new features that may be applicable to match expressions. For example: Get Learning Scala now with the OReilly learning platform. It turns out that expressions are also a good foundation for defining most of Scalas syntax. An expression returns a result, while a statement does not. Patterns can be nested, results of patterns can be bound, and pattern matching can even be user-defined. Using a single expression without an expression block in if..else expressions works well if everything fits on one line. Value binding within the definition of a for-loop makes it possible to centralize most of the loops logic inside the definition. The problem with using if blocks as expressions is that they only conditionally return a value. See the pattern matching examples in the Control Structures chapter for more details. Try experimenting with them to find new ways to express relationships or equivalence through match expressions. In these cases, while loop is used. The only restriction for pattern variable naming, other than the naming requirements already in place for values and variables, is that they must start with a lowercase letter. Why is processing a sorted array faster than processing an unsorted array? An alternate way to do this in Scala is to use value binding in the for-loops definition, which works the same but can help to minimize the size and complexity of the expression block. You can also use one or more if expressions inside a for loop. In a way you can consider this for-loop to be a map, because it takes the expression of rendering the day to a String and applies it for every member of the input range. This loop iterates over the numbers 1 to 3, and for each number it also iterates over the characters a to c. Lets start exploring actual if and if .. else blocks by looking at the syntax for the simple if block. You can combine multiple patterns together with a pattern alternative, where the case block will be triggered if any one of the patterns match.

This example shows (a) how to use a match expression as the body of a method, and (b) how to match all the different types shown: The method getClassAsString takes as a parameter a value of type Matchable, which can be Scala | Loops(while, do..while, for, nested loops), Scala Tutorial Learn Scala with Step By Step Guide, Hello World Program : First program while learning Programming, Scala SortedMap addString() method with a start, a separator and an end with example, Difference Between Traits and Abstract Classes in Scala, Scala | Null, null, Nil, Nothing, None, and Unit, Scala Console | println, printf and readLine, Recursive Streams and collection in Scala, Scala Iterator mkString() method with a start, a separator and an end with example, Scala Map mkString() method with a start, a separator and an end with example, Scala Map addString() method with a start, a separator and an end with example, Scala Iterator addString() method with a start, a separator and an end with example, Scala List addString() method with a start, a separator and an end with example, Scala List mkString() method with a start, a separator and an end with example, How to Reverse keys and values in Scala Map, Overriding Accessors and Mutators in Scala, Scala SortedMap mkString() method with a start, a separator and an end with example, Complete Interview Preparation- Self Paced Course, Data Structures & Algorithms- Self Paced Course. In this example I have a Boolean expression that will return false, but is only checked after the statement has had a chance to run: The while and do/while loops may have their uses, for example if youre reading from a socket and need to continue iterating until there is no more content to read. Depending on the input to the expression, additional actions may be taken besides just returning a value: This match expression prints error messages in case the status is 400 or 500 in addition to returning the message error. The println statement is a good example of including more than one expression in a case block. acknowledge that you have read and understood our, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Scala | Decision Making (if, if-else, Nested if-else, if-else if), Scala String substring() method with example, Scala List contains() method with example.

The code is now cleaner, because the intent of using x to define amount is now obvious. To test this out, in the same directory you created the Hello.scala file, start the Scala REPL and run :load Hello.scala: The :load command is a Scala REPL feature and not actually part of the Scala language. In this section we will cover the basic syntax and uses of match expressions. Its one-line syntax looks like this: In Scala 2, the syntax was a bit different. This new value and type can then be used inside the case block. Then I can reuse them in other ways, or print them out as many times as I need. 465). The condition at which loop stops is called breaking condition.Syntax: Note: To execute following commands use Intellij. The term Boolean expression here indicates an expression that will return either true or false. Again we only have a single command in the iterated expression, so this time we will leave off the curly braces because they are not necessary here: Like a pattern guard in a match expression, an iterator guard (also known as a filter) adds an if expression to an iterator. Terms of service Privacy policy Editorial independence. This means that it returns a value, so you can assign the result to a variable: As youll see throughout this book, all Scala control structures can be used as expressions. A do..while loop is almost same as a while loop. However, Scala offers a number of more expressive and more functional ways to handle loops than while and do/while loops. Heres another example for-loop with separate iterator and iterator guards: Nested iterators are extra iterators added to a for-loop, multiplying the total number of iterations by their iterator count.

However, it cant be accessed inside the case block as a bound value would, and thus the input to the match expression is used to create an informative println statement. Expressions themselves may seem to be an obvious concept, and devoting an entire chapter to them has the appearance of being overly generous to the topic. How APIs can take the pain out of legacy system headaches (Ep.

Here, key point of the while loop is that the loop might not ever run. Here is an example showing the uses of these pipes (|) to collapse a 7-pattern match expression down to only two patterns: So far the examples have left open the possibility that a pattern may not be found that matches the input expression. In fact, most Scala developers prefer match expressions over if .. else blocks because of their expressiveness and concise syntax. The condition was surrounded by parentheses, and It probably wont be easier to read, but reducing code to its shortest form is an art, and a good exercise to learn the language. Given this, lets redefine the syntax for defining values and variables based on expressions. By using this website, you agree with our Cookies Policy. If you have multiple expressions in a case block, convert them to an expression block by wrapping them with curly braces. Well, its more fun to try it out than to explain, so here is an example of a match expression that fails to provide a matching pattern for the input expression: The input of match me didnt match the only given pattern, nope, so the Scala compiler treated this as a runtime error. The match expression was able to match based on the actual type of the value, not just on the type that it was given. The wildcard cannot be accessed on the right side of the arrow, unlike with value binding. Why don't Java's +=, -=, *=, /= compound assignment operators require casting? When the condition is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed. In case this event does occur, for example if the input to the previous example was MONDAY, what do you think would happen? Print the numbers 1 to 100, with each line containing a group of five numbers. An alternate way to execute external Scala files is with the :load command in the Scala REPL. Now that you have the option of developing within the Scala REPL or in a separate text editor or IDE, you can get started with the exercises for this chapter. The preceding example could have been rewritten without the semicolons as follows: Expression blocks are also nestable, with each level of expression block having its own scoped values and variables. We have used this to map the range of numbers from 1 to 7 into a collection of messages of the same size. Statements have a return type of Unit, the type that indicates the lack of a value. However, what if what I really need is a collection of these Day X: messages? Here is another example of a match expression, one that takes an integer status code and tries to return the most appropriate message for it. A common tactic in for-loops is to define temporary values or variables inside the expression block based on the current iteration.

An expression has its own scope, and may contain values and variables local to the expression block. Syntax: Defining Values and Variables, Using Expressions. The following commands are used to compile and execute this program. How to directly initialize a HashMap (in a literal way)?

This is the one class common to both String (which extends AnyRef) and to Unit (which extends AnyVal). Here is an example of using iterator guards to create a collection of numbers that are multiples of 3: An iterator guard can also appear on its own line, separate from the iterator. Scala REPL commands are distinguished from regular Scala syntax by their : prefix.