1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170

//! Easy Address Comparison
//!
//! A set of macros to allow your types to be compared based on where they are stored in memory. This is useful when two instances of a type should not be considered equal unless they are literally the same instance.
//!
//! With this crate, you can derive `AddressEq`, `AddressOrd`, or `AddressHash` depending on your needs.
//!
//! ## Usage
//!
//! ```rust
//! use address_cmp::AddressEq;
//!
//! #[derive(AddressEq, Debug)]
//! struct A {
//!   pub a: u8,
//! }
//!
//! let a1 = A { a: 0 };
//! let a2 = A { a: 0 };
//!
//! assert_ne!(a1, a2);
//! assert_eq!(a1, a1);
//! ```

#[cfg(doc)]
use std::cmp::{Eq, Ord, PartialEq, PartialOrd};
#[cfg(doc)]
use std::hash::Hash;

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, DeriveInput};

/// Derives [`PartialEq`] and [`Eq`] based on memory addresses.
///
/// By deriving [`AddressEq`], the [`PartialEq`] and [`Eq`] traits will automatically be
/// implemented for the given type. The implementations will use a given instance's address
/// in memory in when checking equality.
/// ```rust
/// use address_cmp::AddressEq;
///
/// #[derive(AddressEq, Debug)]
/// struct Person {
///     pub age: u8,
///     pub name: String,
/// }
///
/// let p1 = Person { age: 22, name: "Mercutio".into() };
/// let p2 = Person { age: 22, name: "Mercutio".into() };
///
/// assert_ne!(p1, p2);
/// assert_eq!(p1, p1);
/// ```
#[proc_macro_derive(AddressEq)]
pub fn address_eq(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    let name = &input.ident;
    let lifetime = &input.generics;
    (quote! {
        #[automatically_derived]
        impl #lifetime ::std::cmp::PartialEq for #name #lifetime {
            fn eq(&self, other: &Self) -> bool {
                ::std::ptr::eq(self as *const #name, other as *const #name)
            }
        }

        #[automatically_derived]
        impl #lifetime ::std::cmp::Eq for #name #lifetime {}
    })
    .into()
}

/// Derives [`Hash`] based on memory addresses.
///
/// By deriving [`AddressHash`], the [`Hash`] trait will automatically be
/// implemented for the given type. The implementation will use a given instance's address
/// in memory in when performing hashing.
///
/// Note that since implementations of Hash and Eq must agree, it is recommended to derive both
/// [`AddressHash`] and [`AddressEq`] together.
/// ```rust
/// use address_cmp::{AddressEq, AddressHash};
/// use std::collections::HashSet;
///
/// #[derive(AddressHash, AddressEq)]
/// enum Animal {
///     Bat,
///     Cat,
/// }
///
/// let mut set = HashSet::new();
/// let a1 = Animal::Bat;
/// let a2 = Animal::Cat;
/// let a3 = Animal::Bat;
///
/// set.insert(a1);
/// set.insert(a2);
/// set.insert(a3);
///
/// assert_eq!(set.len(), 3);
/// ```
#[proc_macro_derive(AddressHash)]
pub fn address_hash(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    let name = &input.ident;
    let lifetime = &input.generics;
    (quote! {
        #[automatically_derived]
        impl #lifetime ::std::hash::Hash for #name #lifetime {
            fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
                (self as *const #name).hash(state)
            }
        }
    })
    .into()
}

/// Derives [`PartialOrd`] and [`Ord`] based on memory addresses.
///
/// By deriving [`AddressOrd`], the [`PartialOrd`] and [`Ord`] traits will automatically be
/// implemented for the given type. The implementations will use a given instance's address
/// in memory in when performing comparison.
///
/// This form of comparison can be useful in certain cases, like implementing ordering based
/// on position in a slice, but can also produce unexpected results depending on how the compiler
/// chooses to place data in memory.
///
/// Since implementing [`PartialOrd`] on a type requires that the type also implements [`PartialEq`]
/// and implementations of Hash and Eq must agree, it is recommended to derive both
/// [`AddressOrd`] and [`AddressEq`] together.
/// ```rust
/// use address_cmp::{AddressEq, AddressOrd};
///
/// #[derive(AddressEq, AddressOrd, Debug)]
/// struct Person {
///     pub age: u8,
///     pub name: String,
/// }
///
/// let p1 = Person { age: 22, name: "Mercutio".into() };
/// let p2 = Person { age: 22, name: "Mercutio".into() };
/// let p3 = Person { age: 21, name: "Benvolio".into() };
///
/// let friends = vec![p1, p2, p3];
///
/// assert!(friends[0] < friends[1]);
/// assert!(friends[1] < friends[2]);
/// assert_eq!(friends[0], friends[0]);
/// ```
#[proc_macro_derive(AddressOrd)]
pub fn address_ord(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    let name = &input.ident;
    let lifetime = &input.generics;
    (quote! {
        #[automatically_derived]
        impl #lifetime ::std::cmp::Ord for #name #lifetime {
            fn cmp(&self, other: &Self) -> ::std::cmp::Ordering {
                (self as *const #name).cmp(&(other as *const #name))
            }
        }

        #[automatically_derived]
        impl #lifetime ::std::cmp::PartialOrd for #name #lifetime {
            fn partial_cmp(&self, other: &Self) -> ::std::option::Option<::std::cmp::Ordering> {
                ::std::option::Option::Some(self.cmp(other))
            }
        }
    })
    .into()
}