What is a match statement Rust?
match is a control flow operator in Rust that is used to transfer control to a particular block of code based on the value of the variable being tested. This operator is the equivalent of the switch statement in languages like C++, JavaScript, and Java.
Does Rust have pattern matching?
Patterns are a special syntax in Rust for matching against the structure of types, both complex and simple. Using patterns in conjunction with match expressions and other constructs gives you more control over a program's control flow.
What is an expression match?
A match expression has a scrutinee expression, which is the value to compare to the patterns. The scrutinee expression and the patterns must have the same type. A match behaves differently depending on whether or not the scrutinee expression is a place expression or value expression.
What is if let in Rust?
An if let expression in Rust is slightly different from an if expression in Rust. if let includes the let keyword followed by a pattern, a = sign, and an expression. If the expression matches the pattern, then the following block of code is executed. If it does not match, then the else block of code is executed.
Does Rust have type inference?
As Scala, Rust also has type inference. It's one of the first system level programming language which has support for the type inference.
How do you panic in Rust?
You can override the panic hook using std::panic::set_hook() . Inside the hook a panic can be accessed as a &dyn Any + Send , which contains either a &str or String for regular panic!() invocations. To panic with a value of another other type, panic_any can be used.
What is () in regular expression?
The () will allow you to read exactly which characters were matched. Parenthesis are also useful for OR'ing two expressions with the bar | character. For example, (a-z|0-9) will match one character -- any of the lowercase alpha or digit.
How does regex matching work?
A regex pattern matches a target string. The pattern is composed of a sequence of atoms. An atom is a single point within the regex pattern which it tries to match to the target string. The simplest atom is a literal, but grouping parts of the pattern to match an atom will require using ( ) as metacharacters.
Why regex is used?
Regular Expressions, also known as Regex, come in handy in a multitude of text processing scenarios. Regex defines a search pattern using symbols and allows you to find matches within strings. The applications of this span from software engineering to data science and beyond.
What is Mut in Rust?
mut stands for mutable. You are telling the Rust compiler that you will be changing this variable. What's nice is that Rust holds you to this contract. If you declare a variable using mut and never change it you'll see this warning.
What is Rust unwrap?
To “unwrap” something in Rust is to say, “Give me the result of the computation, and if there was an error, panic and stop the program.” It would be better if we showed the code for unwrapping because it is so simple, but to do that, we will first need to explore the Option and Result types.
What is enum in Rust?
An enum in Rust is a type that represents data that is one of several possible variants. Each variant in the enum can optionally have data associated with it: #![allow(unused_variables)] fn main() { enum Message { Quit, ChangeColor(i32, i32, i32), Move { x: i32, y: i32 }, Write(String), }
Patterns that Bind to Values
Another useful feature of match arms is that they can bind to the parts of the values that match the pattern. This is how we can extract values out of enum variants.
Matches Are Exhaustive
There’s one other aspect of match we need to discuss. Consider this version of our plus_one function that has a bug and won’t compile:
What is the exact form of matching?
The exact form of matching that occurs depends on the pattern . A match expression has a scrutinee expression, which is the value to compare to the patterns. The scrutinee expression and the patterns must have the same type. A match behaves differently depending on whether or not the scrutinee expression is a place expression or value expression .
What are the attributes on match arms?
Attributes on match arms. Outer attributes are allowed on match arms. The only attributes that have meaning on match arms are cfg, cold, and the lint check attributes. Inner attributes are allowed directly after the opening brace of the match expression in the same expression contexts as attributes on block expressions.
Why do match arms use pattern guards?
Match arms can accept match guards to further refine the criteria for matching a case. Pattern guards appear after the pattern and consist of a bool -typed expression following the if keyword. When the pattern matches successfully, the pattern guard expression is executed.
What is a pattern guard?
A pattern guard may refer to the variables bound within the pattern they follow. Before evaluating the guard, a shared reference is taken to the part of the scrutinee the variable matches on. While evaluating the guard, this shared reference is then used when accessing the variable.
default case
In Rust, the default case starts with _ followed by => and default code block. The default code block gets executed when the expression value do not match with any test cases.
Common code blocks
There are instances where same code block is required in multiple cases.
Using if expressions in case statements
Scala gives the flexibility of using if expressions in case statements.
Options That Only Run Codes with Match
We start with a simple Rust match statement example. Consider the following codes. We have two functions that only display texts on the console. Using the match construct, we run these functions depending on a numeric value. Okay, we have the user_choice variable that dictates how the match statement works.
Options That Only Return Values from Match
Now, instead of calling functions or running blocks of codes, the match can return values with a little change in the match contract’s syntax. Notice line 4 in the codes – we use the let keyword together with the match keyword. Cool, no?
Mixing Options That Run Codes With Returning Values
Mixing match options that run codes with those that return values will not work. Let us explore it. Consider the following codes.
Using String and &Str with Match Example
If we are to use string (in lowercase) values in the match statement, we need to use static (or literal) string values. As a result, the argument we pass to the match statement must be of the same type. Consider the following codes.
Using Rust enum With Match Example
Now, for the most exciting part – we can use enums with match statements. Consider the following codes. We have an enum Direction that has NORTH, EAST, WEST, and SOUTH.