[−][src]Crate py_comp
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 prvided in this macro:
- The expression in the beginning of the generator expression must end with a semicolon (;).
- The pattern between the
for
andin
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
for
token (and potentially before anif
token) must evaluate to either anIterator
or animpl IntoIterator
, and end with a semicolon (;). - The conditional expression after the
if
expression expression (and potentially before afor
token) must evaluate to a boolean, and end with a 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.
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))])
Macros
comp | A Python-like lazy generator-expression |