Attribute Macro modifiers 

#[modifiers]

Macro used to add guards to functions. If the guard function returns Ok then execution would continue. If the guard function returns Err the execution would stop and state changes would be reverted by invoking ic_cdk::api::call::reject.

If multiple guard functions exist they’re executed in the order declared.

Usually the modifiers macro should be the last macro declared for a function, below everything else such as update and query. Those are the only macros tested to work together with this modifiers macro. If you would like to use it with other macros or use a different order, remember Rust macro ordering rules apply, and always check the expanded result.

The signatures of guard functions must be of

fn guard_func<T>(param: T) -> Result<(), String>

Then the guard functions can be added as modifiers using the follow syntax:

#[modifiers("guard_func@param", ...)]
fn my_func() {}

The param can be a commma-separated list(without spaces in between) of the arguments.

Examples

#[modifiers("guard_func0")]
fn my_func0() {}
#[modifiers("guard_func@42,SomeEnum::A")]
fn my_func1() {}
#[modifiers("guard_func0", "guard_func1")]
fn my_func2() {}