Derive Macro structmeta::ToTokens

#[derive(ToTokens)]
{
    // Attributes available to this derive:
    #[to_tokens]
}

Derive quote::ToTokens for syntax tree node.

• Example
• Helper attributes
  • #[to_tokens("[", "]", "(", ")", "{", "}"]
  • #[to_tokens(dump)]

Example

#[derive(ToTokens)] generates an implementation of ToTokens that calls ToTokens::to_tokens for each field.

use syn::LitInt;

#[derive(structmeta::ToTokens)]
struct Example(LitInt, LitInt);

Code like this will be generated:

impl quote::ToTokens for Example {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        self.0.to_tokens(tokens);
        self.1.to_tokens(tokens);
    }
}

#[derive(ToTokens)] can also be specified for enum.

use syn::{LitInt, LitStr};

#[derive(structmeta::ToTokens)]
enum Example {
    A(LitInt),
    B(LitStr),
}

Code like this will be generated:

impl quote::ToTokens for Example {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        match self {
            Self::A(l) => l.to_tokens(tokens),
            Self::B(l) => l.to_tokens(tokens),
        }
    }
}

Helper attributes

	struct	enum	variant	field
#[to_tokens("[")], #[to_tokens("]")]				✔
#[to_tokens("(")], #[to_tokens(")")]				✔
#[to_tokens("{")], #[to_tokens("}")]				✔
#[to_tokens(dump)]	✔	✔

#[to_tokens("[", "]", "(", ")", "{", "}"]

By specifying #[to_tokens("[")] or #[to_tokens("(")] or #[to_tokens("[")] , subsequent tokens will be enclosed in [] or () or {}.

By default, all subsequent fields are enclosed. To restrict the enclosing fields, specify #[to_tokens("]")] or #[to_tokens(")")] or #[to_tokens("}")] for the field after the end of the enclosure.

use syn::{token, LitInt};

#[derive(structmeta::ToTokens)]
struct Example {
    x: LitInt,
    #[to_tokens("[")]
    bracket_token: token::Bracket,
    y: LitInt,
    #[to_tokens("]")]
    z: LitInt,
}

Code like this will be generated:

impl quote::ToTokens for Example {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        self.x.to_tokens(tokens);
        token::Bracket::surround(&self.bracket_token, tokens, |tokens| {
            self.y.to_tokens(tokens);
        });
        self.z.to_tokens(tokens);
    }
}

If the field type is Bracket or Paren or Brace, the symbol corresponding to the token type must be specified.

If the field type is MacroDelimiter, any symbol can be used and there is no difference in behavior. (Three types of parentheses are available, no matter which symbol is specified.)

field type	start	end
syn::token::Bracket	"["	"]"
syn::token::Paren	"("	")"
syn::token::Brace	"{"	"}"
syn::MacroDelimiter	"[" or "(" or "{"	"]" or ")" or "}"

#[to_tokens(dump)]

Causes a compile error and outputs the code generated by #[derive(ToTokens)] as an error message.