castflip_derive 0.1.3

Derive macros for castflip
Documentation 
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use proc_macro::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Fields, FieldsNamed, FieldsUnnamed, Ident};


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) =>
		    proc_named_struct(&ast.ident, &fields_named),
		Fields::Unnamed(fields_unnamed) =>
		    proc_unnamed_struct(&ast.ident, &fields_unnamed),
		Fields::Unit =>
		    proc_unit_struct(&ast.ident),
	    },
	Data::Enum(_data_enum) =>
	    panic!("Trait Flip cannot be implemented for enum."),
	Data::Union(_data_union) =>
	    panic!("Trait Flip cannot be implemented for union."),
    }
}

// e.g. struct Ident { field1: Type1, field2: Type2, ... }
fn proc_named_struct(ident: &Ident, fields: &FieldsNamed) -> TokenStream {
    let field_type = fields.named.iter().map(|field| &field.ty);
    let field_name1 = fields.named.iter().map(|field| &field.ident);
    let field_name2 = fields.named.iter().map(|field| &field.ident);
    let field_name3 = fields.named.iter().map(|field| &field.ident);

    quote! {
	impl castflip::Flip for #ident
	where
	    #( #field_type: castflip::Flip, )*
	{
	    fn flip_val_swapped(&self) -> Self {
		Self {
		    #(
			#field_name1: self. #field_name2 .flip_val_swapped(),
		    )*
		}
	    }
	    fn flip_var_swapped(&mut self) {
		#(
		    self. #field_name3 .flip_var_swapped();
		)*
	    }
	}
    }.into()
}

// e.g. struct Ident ( Type1, Type2, ... );
fn proc_unnamed_struct(ident: &Ident, fields: &FieldsUnnamed) -> TokenStream {
    let field_type = fields.unnamed.iter().map(|field| &field.ty);
    let field_index1 = ( 0 .. fields.unnamed.len() ).map(syn::Index::from);
    let field_index2 = ( 0 .. fields.unnamed.len() ).map(syn::Index::from);

    quote! {
	impl castflip::Flip for #ident
	where
	    #( #field_type: castflip::Flip, )*
	{
	    fn flip_val_swapped(&self) -> Self {
		Self (
		    #(
			self. #field_index1 .flip_val_swapped(),
		    )*
		)
	    }
	    fn flip_var_swapped(&mut self) {
		#(
		    self. #field_index2 .flip_var_swapped();
		)*
	    }
	}
    }.into()
}

// e.g. struct Ident;
fn proc_unit_struct(ident: &Ident) -> TokenStream {
    quote! {
	impl castflip::Flip for #ident
	{
	    fn flip_val_swapped(&self) -> Self {
		Self
	    }
	    fn flip_var_swapped(&mut self) {}
	}
    }.into()
}