Derive Macro trustfall_derive::TrustfallEnumVertex

#[derive(TrustfallEnumVertex)]
{
    // Attributes available to this derive:
    #[trustfall]
}

Adds the Typename trait and as_<variant>() methods on an enum used as a Trustfall vertex.

For example:

#[derive(Debug, Clone, TrustfallEnumVertex)]
enum Vertex {
    User(String),
    Message { author: String, content: String },
    EmptyVariant,
}

will get the following implementations:

impl Typename for Vertex {
    fn typename(&self) -> &'static str {
        match self {
            Self::User { .. } => "User",
            Self::Message { .. } => "Message",
            Self::EmptyVariant { .. } => "EmptyVariant",
        }
    }
}

impl Vertex {
    fn as_user(&self) -> Option<&String> {
        match self {
            Self::User(x) => Some(x),
            _ => None,
        }
    }

    fn as_message(&self) -> Option<(&String, &String)> {
        match self {
            Self::Message { author, content } => Some((author, content)),
            _ => None,
        }
    }

    fn as_empty_variant(&self) -> Option<()> {
        match self {
            Self::EmptyVariant => Some(()),
            _ => None,
        }
    }
}

A variant can opt out of having a generated conversion method using the #[trustfall(skip_conversion)] attribute.

In this example, only the User variant gets a conversion method:

#[derive(Debug, Clone, TrustfallEnumVertex)]
enum Vertex {
    User(String),

    #[trustfall(skip_conversion)]
    Message { author: String, content: String },
}

To add only the Typename implementation without the as_<variant>() conversions, use the Typename derive macro instead.