macro_rules! todo {
() => { ... };
($($arg:tt)+) => { ... };
}
Expand description
Indicates unfinished code.
This can be useful if you are prototyping and are just looking to have your code typecheck.
The difference between unimplemented!
and todo!
is that while todo!
conveys
an intent of implementing the functionality later and the message is “not yet
implemented”, unimplemented!
makes no such claims. Its message is “not implemented”.
Also some IDEs will mark todo!
s.
Panics
This will always panic!
.
Examples
Here’s an example of some in-progress code. We have a trait Foo
:
trait Foo {
fn bar(&self);
fn baz(&self);
}
RunWe want to implement Foo
on one of our types, but we also want to work on
just bar()
first. In order for our code to compile, we need to implement
baz()
, so we can use todo!
:
struct MyStruct;
impl Foo for MyStruct {
fn bar(&self) {
// implementation goes here
}
fn baz(&self) {
// let's not worry about implementing baz() for now
todo!();
}
}
fn main() {
let s = MyStruct;
s.bar();
// we aren't even using baz(), so this is fine.
}
Run