Convert string into TokenStream

问题

Given a string (str), how can one convert that into a TokenStream in Rust?

I've tried using the quote! macro.

let str = "4";
let tokens = quote! { let num = #str; }; // #str is a str not i32

The goal here is to generate tokens for some unknown string of code.

let thing = "4";
let tokens = quote! { let thing = #thing }; // i32

or

let thing = ""4"";
let tokens = quote! { let thing = #thing }; // str

回答1:

how can one convert [a string] into a TokenStream

Rust has a common trait for converting strings into values when that conversion might fail: FromStr. This is usually accessed via the parse method on &str.

proc_macro2::TokenStream

use proc_macro2; // 0.4.24

fn example(s: &str) {
    let stream: proc_macro2::TokenStream = s.parse().unwrap();
}

proc_macro::TokenStream

extern crate proc_macro;

fn example(s: &str) {
    let stream: proc_macro::TokenStream = s.parse().unwrap();
}

You should be aware that this code cannot be run outside of the invocation of an actual procedural macro.

来源：https://stackoverflow.com/questions/54165117/convert-string-into-tokenstream