CODEWITHSUNDEEP
rustrust-macrosrust-decl-macros
HentaiMew
HentaiMew

Reputation: 337

Generate attribute value via macro

Suppose I have an ident input parameter named module_name. How can I generate the value of the attribute through this parameter?

In simple terms, I want to generate something like this:

macro_rules! import_mod {
    ( $module_name:ident ) => {
        // This does not work,
        // but I want to generate the value of the feature attribute.
        // #[cfg(feature = $module_name)]
        pub mod $module_name;
    }
}

import_mod!(module1);

// #[cfg(feature = "module1")]
// pub mod module1;

Upvotes: 1

Views: 531

Answers (1)

chub500
chub500

Reputation: 760

The argument in the compiler directive must be a literal.

One half decent work-around is to take a literal as well as your 'feature':

macro_rules! my_import {
    ( $module_name:ident, $feature_name:literal ) => {
        #[cfg(feature = $feature_name)]
        mod $module_name;
    }
}

my_import!(foo, "foo");

For reference - https://doc.rust-lang.org/stable/reference/attributes.html#meta-item-attribute-syntax

To summarize: most built in attributes have the rule #[<attribute> = <literal>]

Upvotes: 1

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