Control Flow
if
expressions
Sway supports if, else, and else if expressions that allow you to branch your code depending on conditions.
For example:
fn main() {
let number = 6;
if number % 4 == 0 {
// do something
} else if number % 3 == 0 {
// do something else
} else {
// do something else
}
}
Using if
in a let
statement
Like Rust, if
s are expressions in Sway. What this means is you can use if
expressions on the right side of a let
statement to assign the outcome to a variable.
let my_data = if some_bool < 10 { foo() } else { bar() };
Note that all branches of the if
expression must return a value of the same type.
match
expressions
Sway supports advanced pattern matching through exhaustive match
expressions.
script;
fn foo() {
// do something
}
fn bar() {
// do something
}
enum SomeEnum {
A: u64,
B: bool,
C: b256,
}
fn main() -> u64 {
let x = 5;
// Match as an expression.
let a = match 8 {
7 => {
4
},
9 => {
5
},
8 => {
6
},
_ => {
100
},
};
// Match as a statement for control flow.
match x {
5 => {
foo()
},
_ => {
bar()
},
};
// Match an enum
let e = SomeEnum::A(42);
let v = match e {
SomeEnum::A(val) => {
val
},
SomeEnum::B(true) => {
1
},
SomeEnum::B(false) => {
0
},
_ => {
0
},
};
// Match as expression used for a return.
match 42 {
0 => {
24
},
foo => {
foo
},
}
}
In the example above, braces around the code block following =>
in each match arm are not required unless the code block contains multiple statements. They are added in this example due to an issue in the Sway formatter.
Loops
while
Loops in Sway are currently limited to while
loops. This is what they look like:
while counter < 10 {
counter = counter + 1;
}
You need the while
keyword, some condition (value < 10
in this case) which will be evaluated each iteration, and a block of code inside the curly braces ({...}
) to execute each iteration.
break
and continue
There are no break
or continue
keywords yet, but they're coming.
For now, the way to break out of a while
loop early is to manually invalidate the condition. In this case, that just means setting counter
to be >= 10
.
Building on the previous example, here's what that might look like:
let mut counter = 0;
let mut break_early = false;
while counter < 10 {
if break_early == true {
// here we ensure the condition will evaluate to false, breaking the loop
counter = 10
} else {
// calling some other function to set the bool value
break_early = get_bool_value();
counter = counter + 1;
}
}
Nested loops
You can also use nested while
loops if needed:
while condition_1 == true {
// do stuff...
while condition_2 == true {
// do more stuff...
}
}