I want to call a function if a condition is met and return multiple values that will be used outside the scope of the conditional block. If the function were only to return one value I would declare the variable at an appropriate earlier point, but as far as I can tell Rust does not allow for assignment of multiple variables unless these variables are also being declared.
Is there a way around this?
Here's some pseudo-code to illustrate my question:
// This approach doesn't work for scope reasons
fn function(inp1, inp2) {
calculate results;
(var_a, var_b, var_c)
}
fn main() {
let state = true;
if state == true {
let (var_a, var_b, var_c) = function(input_1, input_2);
}
do something with var_a, var_b, and var_c;
}
// This approach works when returning one variable
fn function(inp1, inp2) {
calculate results;
var_a
}
fn main() {
let var_a;
let state = true;
if state == true {
var_a = function(input_1, input_2);
}
do something with var_a;
}
In general you can use that approach to solve it (note commented if
statement, explained below):
fn function() -> (i32, i32) {
return (42, 54);
}
fn main() {
//let state = true;
let v: (i32, i32);
//if state == true {
{
v = function();
}
let (var_a, var_b) = v;
println!("a:{} b:{}", var_a, var_b);
}
If you would like to keep the if
in place then else
branch should be provided as well. Otherwise there will be an error like:
error[E0381]: use of possibly-uninitialized variable: `v`
--> src/main.rs:16:10
|
16 | let (var_a, var_b) = v;
| ^^^^^ use of possibly-uninitialized `v.0`
That error don't have any relation with "returning a tuple". The same error come even for the provided 'one variable' example ( playground ).
The final solution may looks like:
fn function() -> (i32, i32) {
return (42, 54);
}
const DEFAULT: (i32, i32) = (0, 0);
fn main() {
let state = true;
let v: (i32, i32);
if state == true {
v = function();
} else {
v = DEFAULT;
}
let (var_a, var_b) = v;
println!("a:{} b:{}", var_a, var_b);
}
PS I personally prefer to move the state
's check inside the function
to simplify the code.
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