Is it possible to conditionally enable an attribute like `derive`?
I have added a feature in my crate which adds serde
support. However, I don't quite understand how to use it properly:
// #[derive(Debug, Serialize, Deserialize, Clone)] // goes to:
#[derive(Debug, Clone)]
#[cfg(feature = "serde_support")]
#[derive(Serialize, Deserialize)]
pub struct MyStruct;
This code treats everything below cfg(feature)
as conditionally compiled, so without my serde_support
feature my crate does not have MyStruct
also.
I have tried to wrap it with braces but it gives another error:
Code:
#[derive(Debug, Clone)]
#[cfg(feature = "serde_support")] {
#[derive(Serialize, Deserialize)]
}
pub struct MyStruct;
Error:
error: expected item after attributes
--> mycrate/src/lib.rs:65:33
|
65 | #[cfg(feature = "serde_support")] {
| ^
So how to do this?
You can use the cfg_attr(a, b)
attribute:
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde_support", derive(Serialize, Deserialize))]
pub struct MyStruct;
It's described in the Rust reference about "conditional compilation":
#[cfg_attr(a, b)] item
Will be the same as
#[b] item
ifa
is set bycfg
, anditem
otherwise.