是否可以在宏内修改令牌的大小写? [英] Is it possible to modify the case of a token inside of a macro?

问题描述

我正在编写一个宏来创建一个管理用户输入的结构.我正在使用板条箱 bitflags 和 sdl2.Return 是键 Return 的示例.

I am writing a macro which creates a struct managing user input. I am using the crates bitflags and sdl2. Return is an example for the key Return.

此宏获取所有可能输入的列表，然后

This macro takes a list of all possible inputs and then

($($flag:ident = $value:expr;)+)  => { ... }

1. 使用输入的名称创建一个新的位标志

1. Creates a new bitflag with the name of the input

bitflags!(
    struct KeyType: u64 {
    $(
        const $flag = $value;// UPPER_CASE is the norm for globals: 'RETURN'
    )+
    }
);

检查按键是否被按下，使用 键码枚举.

match event {
    $(Event::KeyDown { keycode: Some(Keycode::$flag), .. } => { 
        self.flags.insert($flag); 
    },)+
     _ => ()
}// All enum fields start with a capital letter: 'Return'

创建一个getter函数:

Creates a getter function:

$(
    pub fn $flag(&self) -> bool { // lower_case is the norm for functions: 'return'
        self.flags.contains($flag)
    }
)+

我可以调整 $flag 以适应所有三个要求(flag、Flag、FLAG)吗?

Can I adapt $flag to fit all three requirements (flag, Flag, FLAG)?

推荐答案

Macro_rules 宏不能做到这一点.您需要将其实现为过程宏，允许执行任意 Rust 代码以生成扩展代码.特别是，过程宏能够调用 str::to_uppercase 和 str::to_lowercase.

Macro_rules macros cannot do this. You would need to implement it as a procedural macro, which is allowed to perform arbitrary Rust code to generate the expanded code. In particular, procedural macros are able to call str::to_uppercase and str::to_lowercase.

// [dependencies]
// quote = "1.0"
// syn = "1.0"

use proc_macro::TokenStream;
use quote::quote;
use syn::parse::{Parse, ParseStream, Result};
use syn::{parse_macro_input, Expr, Ident, Token};

struct Input {
    flags: Vec<Ident>,
    values: Vec<Expr>,
}

// $( $flag:ident = $value:expr; )*
impl Parse for Input {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut flags = Vec::new();
        let mut values = Vec::new();
        while !input.is_empty() {
            flags.push(input.parse()?);
            input.parse::<Token![=]>()?;
            values.push(input.parse()?);
            input.parse::<Token![;]>()?;
        }
        Ok(Input { flags, values })
    }
}

#[proc_macro]
pub fn sleeping_panda(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as Input);

    let camelcase_flags = &input.flags; // assume CamelCase in the input
    let bitflag_values = &input.values;

    let uppercase_flags = input
        .flags
        .iter()
        .map(|ident| Ident::new(&ident.to_string().to_uppercase(), ident.span()));
    // Some copies because these need to appear multiple times in the generated code.
    let uppercase_flags2 = uppercase_flags.clone();
    let uppercase_flags3 = uppercase_flags.clone();

    let lowercase_flags = input
        .flags
        .iter()
        .map(|ident| Ident::new(&ident.to_string().to_lowercase(), ident.span()));

    TokenStream::from(quote! {
        bitflags::bitflags! (
            struct KeyType: u64 {
                #(
                    const #uppercase_flags = #bitflag_values;
                )*
            }
        );

        pub struct SleepingPanda {
            flags: KeyType,
        }

        impl SleepingPanda {
            pub fn receive_event(&mut self, event: sdl2::event::Event) {
                match event {
                    #(
                        sdl2::event::Event::KeyDown {
                            keycode: Some(sdl2::keyboard::Keycode::#camelcase_flags),
                            ..
                        } => {
                            self.flags.insert(KeyType::#uppercase_flags2);
                        }
                    )*
                    _ => {}
                }
            }

            #(
                pub fn #lowercase_flags(&self) -> bool {
                    self.flags.contains(KeyType::#uppercase_flags3)
                }
            )*
        }
    })
}

使用宏:

use sleeping_panda::sleeping_panda;

sleeping_panda! {
    Backspace = 8;
    Tab = 9;
}

fn main() {}

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