castflip_derive 0.1.13

Derive macros for the castflip crate
Documentation 
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use proc_macro::TokenStream;
use quote::quote;
use syn::{
    Data, DeriveInput, Field, Fields, Ident,
    punctuated::Punctuated, token::Comma,
};


pub fn proc_tokens(input: TokenStream) -> TokenStream {
    // Parse TokenStream into the Rust Abstract Syntax Tree (AST).
    let ast: DeriveInput = syn::parse(input).unwrap();

    match &ast.data {
        Data::Struct(data_struct) =>
            match &data_struct.fields {
                Fields::Named(fields_named) =>
                    with_bounds(&ast.ident, &fields_named.named),
                Fields::Unnamed(fields_unnamed) =>
                    with_bounds(&ast.ident, &fields_unnamed.unnamed),
                Fields::Unit =>
                    without_bounds(&ast.ident),
            },
        Data::Enum(_data_enum) =>
            panic!("The derive macro NopFlip does not support enum."),
        Data::Union(data_union) =>
            with_bounds(&ast.ident, &data_union.fields.named),
    }
}

fn with_bounds(
    ident: &Ident,
    punctuated: &Punctuated<Field, Comma>,
) -> TokenStream {
    let field_type = punctuated.iter().map(|field| &field.ty);

    quote! {
        impl castflip::Flip for #ident
        where
            #( #field_type: castflip::Flip, )*
        {
            fn flip_val_swapped(&self) -> Self {
                unsafe {
                    ::core::ptr::read(self)
                }
            }
            fn flip_var_swapped(&mut self) {}
        }
        impl castflip::NopFlip for #ident {}
    }.into()
}

fn without_bounds(ident: &Ident) -> TokenStream {
    quote! {
        impl castflip::Flip for #ident {
            fn flip_val_swapped(&self) -> Self {
                unsafe {
                    ::core::ptr::read(self)
                }
            }
            fn flip_var_swapped(&mut self) {}
        }
        impl castflip::NopFlip for #ident {}
    }.into()
}