Rust conditionals: Difference between revisions
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</blockquote><!-- Matching Option --> | </blockquote><!-- Matching Option --> | ||
</blockquote><!-- Pattern Matching --> | </blockquote><!-- Pattern Matching --> | ||
= if let = | |||
<blockquote> | |||
if let is essentially a one-branch <code>match</code>, only caring about the value if it is non-none.<br> | |||
if <code>my_value</code> is <code>None</code>, then it returns <code>None</code> and the block does not run. | |||
<syntaxhighlight lang="rust"> | |||
if let Some(x) = my_value { | |||
println!("The value {} was bound!!", x); | |||
} | |||
</syntaxhighlight> | |||
</blockquote><!-- if let --> |
Revision as of 22:09, 7 February 2023
if statement
if num < 5 { // .. } else if { // .. } else { // .. }
assign if
let weather = if season == "fall" { "lovely" } else { "fine I guess" } // ternary operator
match
Basics
Like a switch statement,
but the compiler ensures the entire valid range of items is checked for.
especially useful for enums.In the following case, if
_
was omitted
you'd need to ensure the full range of possible i32 numbers were supported!.// if num is '1', returns 'a' // if num is >2, returns 'c' let result = match num { 1 => "a", 2 => "b", _ => "c", // anything other than 1 or 2 }You can match multiple values
let result = match num { 1 | 3 | 5 => "one three or five", _ => "something else" }Matching Enums
When matching a parametrized enum, you can access the tuple/struct/value that is bound to it
enum Pet { Cat(String, u8), Dog{name: String, age: u8}, Lizard(u8), } let pet = Pet::Lizard(5); match pet { Pet::Cat(name, age) => { format!("cat, name={}, age={}", name, age) }, Pet::Dog(dog) => { format!("dog, name={dog.name}, age={dog.age}") }, Pet::Lizard(age) => { format!("lizard, age={}", age) } }Matching Option
Option is just an enum, generally if you don't have a specific behaviour for
None
,
you return a newNone
in that branch.
However this an opportunity to fail if it is an appropriate location for it.match some_value { Some(x) => "you received a value!", None => None, }
if let
if let is essentially a one-branch
match
, only caring about the value if it is non-none.
ifmy_value
isNone
, then it returnsNone
and the block does not run.if let Some(x) = my_value { println!("The value {} was bound!!", x); }