Macro syn::parse_macro_input [−][src]
Parse the input TokenStream of a macro, triggering a compile error if the tokens fail to parse.
Refer to the parse
module documentation for more details about parsing
in Syn.
Intended usage
This macro must be called from a function that returns
proc_macro::TokenStream
. Usually this will be your proc macro entry point,
the function that has the #[proc_macro] / #[proc_macro_derive] /
#[proc_macro_attribute] attribute.
use proc_macro::TokenStream; use syn::{parse_macro_input, Result}; use syn::parse::{Parse, ParseStream}; struct MyMacroInput { /* ... */ } impl Parse for MyMacroInput { fn parse(input: ParseStream) -> Result<Self> { /* ... */ } } #[proc_macro] pub fn my_macro(tokens: TokenStream) -> TokenStream { let input = parse_macro_input!(tokens as MyMacroInput); /* ... */ }
Usage with Parser
This macro can also be used with the Parser
trait for types that have
multiple ways that they can be parsed.
impl MyMacroInput { fn parse_alternate(input: ParseStream) -> Result<Self> { /* ... */ } } #[proc_macro] pub fn my_macro(tokens: TokenStream) -> TokenStream { let input = parse_macro_input!(tokens with MyMacroInput::parse_alternate); /* ... */ }
Expansion
parse_macro_input!($variable as $Type)
expands to something like:
match syn::parse::<$Type>($variable) { Ok(syntax_tree) => syntax_tree, Err(err) => return proc_macro::TokenStream::from(err.to_compile_error()), }