Hi, I am trying to create a macro_rules to help generate a function, which reduce many duplicated code. The function is just simple setters/getters.

Here's the example:

It is actually not the real code in my project, but I try to create a minimal example that can reproduce my question.

And one more thing, let's ignore the details about struct OptionBuilder in below example, it doesn't matter.

#[macro_export]
macro_rules! builder_impl {
  ($member:ident,$flags:ident,$($field:ident),+) => {
    paste::paste! {
      impl OptionBuilder {
        $(
          pub fn $field(&mut self, value: bool) -> &mut Self {
            let mut flags = self.$member.unwrap_or( [< $member:upper >] );
            flags.set( [<  $flags :: $field:upper >] , value);
            self.$member = Some(flags);
            self
          }
        )+
      }
    }
  }
}

I will use this macro like this:

struct Flags {
  const EXPAND_TAB = 1;
}
const FLAGS: Flags = Flags {};

builder_impl!(flags, Flags, expand_tab);

And it should generate source code:

impl OptionBuilder {
  pub fn expand_tab(&mut self, value: bool) -> &mut Self {
    let mut flags = self.flags.unwrap_or( FLAGS );
    flags.set( Flags::EXPAND_TAB , value);  <-- Compiler complains about the double colons in "Flags::EXPAND_TAB"
    self.flags = Some(flags);
    self
  }
}

The error comes from the double colons in the Flags::EXPAND_TAB, it seems paste! macro thinks the :: is other things.

How should I fix this?

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