[−][src]Crate try_match
Provides an expression macro try_match
that performs pattern
matching and returns the bound variables via Ok(_)
iff successful.
Examples
Explicit Mapping
use try_match::try_match; #[derive(Copy, Clone, Debug, PartialEq)] enum Enum<T> { Var1(T), Var2 } use Enum::{Var1, Var2}; // The right-hand side of `=>` if successful assert_eq!(try_match!(Var1(x) = Var1(42) => x), Ok(42)); assert_eq!(try_match!(Var2 = Var2::<u32> => "yay"), Ok("yay")); // `Err(input)` on failure assert_eq!(try_match!(Var1(x) = Var2::<u32> => x), Err(Var2)); assert_eq!(try_match!(Var2 = Var1(42) => "yay"), Err(Var1(42)));
Implicit Mapping
=>
and the part that comes after can be omitted (requires implicit_map
feature, which is enabled by default; you can disable it to skip the
compilation of the internal procedural macro):
// `()` if there are no bound variables assert_eq!(try_match!(Var1(_) = Var1(42)), Ok(())); // The bound variable if there is exactly one bound variables assert_eq!(try_match!(Var1(x) = Var1(42)), Ok(42)); // An anonymous struct if there are multiple bound variables let vars = try_match!(Var1((a, b)) = Var1((12, 34))).unwrap(); assert_eq!((vars.a, vars.b), (12, 34));
It produces a tuple if you name the bound variables like _0
, _1
, _2
,
...:
let (a, b) = try_match!(Var1((_0, _1)) = Var1((12, 34))).unwrap(); assert_eq!((a, b), (12, 34));
It's an error to specify non-contiguous binding indices:
ⓘThis example deliberately fails to compile
let _ = try_match!(Var1((_0, _2)) = Var1((12, 34)));
ⓘThis example deliberately fails to compile
let _ = try_match!(Var1((_0, _9223372036854775808)) = Var1((12, 34)));
Restrictions
- Macros cannot be used in a supplied pattern.
Related Work: matches
matches!
is similar but only returns bool
indicating whether matching
was successful or not.
let success1 = matches!(Var1(42), Var1(_));
let success2 = try_match!(Var1(_) = Var1(42)).is_ok();
Macros
try_match | Try to match |