try_match

Provides an expression macro try_match that performs pattern matching and returns the bound variables via Ok(_) iff successful.

Examples

Explicit Mapping

```rust use trymatch::trymatch;

[derive(Copy, Clone, Debug, PartialEq)]

enum Enum { Var1(T), Var2 } use Enum::{Var1, Var2};

// The right-hand side of => if successful asserteq!(trymatch!(Var1(x) = Var1(42) => x), Ok(42)); asserteq!(trymatch!(Var2 = Var2:: => "yay"), Ok("yay"));

// Err(input) on failure asserteq!(trymatch!(Var1(x) = Var2:: => x), Err(Var2)); asserteq!(trymatch!(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):

``rust //()` if there are no bound variables asserteq!(trymatch!(Var1(_) = Var1(42)), Ok(()));

// The bound variable if there is exactly one bound variables asserteq!(trymatch!(Var1(x) = Var1(42)), Ok(42));

// An anonymous struct if there are multiple bound variables let vars = trymatch!(Var1((a, b)) = Var1((12, 34))).unwrap(); asserteq!((vars.a, vars.b), (12, 34)); ```

It produces a tuple if you name the bound variables like _0, _1, _2, ...:

rust 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:

rust let _ = try_match!(Var1((_0, _2)) = Var1((12, 34)));

rust 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.

rust let success1 = matches!(Var1(42), Var1(_)); let success2 = try_match!(Var1(_) = Var1(42)).is_ok();

License: MIT/Apache-2.0