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//! This macro implements a syntax that emulates Pythons //! [`generator-expression`] syntax in a form more compatible with rusts //! usual syntax. //! //! This means that there a few small differences between the python syntax //! and the syntax provided in this macro: //! //! * The pattern between the `for` and `in` tokens is a fully-fledged //! rust pattern, which can be as simple as a simple token and as complex //! as struct destructuring. //! * The expression defining the iterator after the `in` token //! must evaluate to either an `Iterator` or an `impl IntoIterator`. //! * The conditional expression after the `if` token must evaluate to //! a boolean. //! * The expression in the beginning of the generator expression, //! the expression following the `in` token, and the expression following //! the `if` token, must all end with a semicolon (;). The only exception //! to this is the last expression following `in` or `if` in the macro, //! which may omit the trailing semicolon. //! //! The expression replaced by the `comp!()` macro invocation is a lazy //! iterator whose lifetime is bound by any references it needs to capture. //! This means that it can be `.collect()`ed into any container you like. //! //! This is a BNF description of the syntax used by this macro: //! //! ```bnf //! comprehension ::= expression ";" comp_for [";"] //! comp_for ::= "for" pattern "in" expression [";" comp_iter] //! comp_iter ::= comp_for | comp_if //! comp_if ::= "if" expression [";" comp_iter] //! ``` //! //! Just like in Python, you can nest as many `for` and `if` //! clauses as you like. //! //! # Examples //! //! Simple generator expression with a conditional: //! ``` //! use py_comp::comp; //! //! #[derive(Debug, PartialEq, Eq)] //! struct Foo(i32); //! //! let arr = &[Foo(11), Foo(12)]; //! //! // Notice the semicolons //! let comp_vector = comp!(item; for item in arr; if item.0 % 10 == 2) //! .collect::<Vec<&Foo>>(); //! //! assert_eq!(comp_vector, vec![&Foo(12)]) //! ``` //! //! Triple cartesian product with conditions and patterns: //! ``` //! use py_comp::comp; //! //! #[derive(Debug, PartialEq, Eq)] //! struct Foo(i32); //! //! // These need to be references to arrays because of how the closures //! // that the macro expands to capture their environment. //! let x = &[(Foo(11), "foo"), (Foo(12), "bar")]; //! let y = &[Foo(21), Foo(22)]; //! let z = &[Foo(31), Foo(32)]; //! //! let xyz = comp!( //! (a, b, c); //! for (a, _text) in x; // You can use any function parameter pattern. //! if a.0 % 10 == 2; //! for b in y; // Obviously not every level requires a conditional. //! for c in z; //! if c.0 % 10 == 2; //! ) //! .collect::<Vec<(&Foo, &Foo, &Foo)>>(); //! //! // The result vector here is short for illustration purposes //! // but can be as long as long as you need it to be. //! assert_eq!(xyz, vec![(&Foo(12), &Foo(21), &Foo(32)), (&Foo(12), &Foo(22), &Foo(32))]) //! ``` //! Flatten a triple-nested structure + complex expression: //! ```rust //! use py_comp::comp; //! //! #[derive(Debug, PartialEq, Eq)] //! struct Foo(i32); //! //! let nested_3 = &[ //! [ //! [Foo(0), Foo(1), Foo(2)], //! [Foo(3), Foo(4), Foo(5)], //! [Foo(6), Foo(7), Foo(8)], //! ], //! [ //! [Foo(9), Foo(10), Foo(11)], //! [Foo(12), Foo(13), Foo(14)], //! [Foo(15), Foo(16), Foo(17)], //! ], //! [ //! [Foo(18), Foo(19), Foo(20)], //! [Foo(21), Foo(22), Foo(23)], //! [Foo(24), Foo(25), Foo(26)], //! ], //! ]; //! //! let nested_objects = comp!( //! { //! let inner = nested.0; //! Foo(inner + 1) //! }; //! for nested_2 in nested_3; //! for nested_1 in nested_2; //! for nested in nested_1; //! ) //! .collect::<Vec<Foo>>(); //! //! let expected_values = (1..28).map(Foo).collect::<Vec<Foo>>(); //! //! assert_eq!(expected_values, nested_objects); //! ``` //! //! [`generator-expression`]: https://docs.python.org/3/reference/expressions.html#generator-expressions //! #![warn(clippy::all)] use doc_comment::doctest; doctest!("../Readme.md"); // Check that the type of the expression passed here implements IntoIterator. // Hopefully this optimizes away in release builds. #[doc(hidden)] #[macro_export] macro_rules! assert_impl_into_iter { ($x: expr) => { let _ = || { fn assert_impl_into_iter<T>(_: T) where T: IntoIterator, { } assert_impl_into_iter($x); }; }; } /// A Python-like lazy generator-expression /// /// For details see [module level documentation][super] /// /// [super]: ../py_comp/index.html #[macro_export(local_inner_macros)] macro_rules! comp { ( $item_expr: expr; for $name: pat in $iterator: expr; if $condition: expr $(;)? ) => {{ let iter = $iterator; $crate::assert_impl_into_iter!(iter); iter .into_iter() .filter_map(move |$name| if $condition { Some($item_expr) } else { None } ) }}; ( $item_expr: expr; for $name: pat in $iterator: expr $(;)? ) => {{ let iter = $iterator; $crate::assert_impl_into_iter!(iter); iter .into_iter() .map(move |$name| $item_expr) }}; ( $item_expr: expr; for $name: pat in $iterator: expr; if $condition: expr; for $($rest: tt)* ) => {{ let iter = $iterator; $crate::assert_impl_into_iter!(iter); iter .into_iter() .filter_map(move |$name| if $condition { Some(comp!($item_expr; for $($rest)*)) } else { None } ) .flatten() }}; ( $item_expr: expr; for $name: pat in $iterator: expr; for $($rest: tt)* ) => {{ let iter = $iterator; $crate::assert_impl_into_iter!(iter); iter .into_iter() .flat_map(move |$name| comp!($item_expr; for $($rest)*) ) }}; }