[−][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:

`let _ = try_match!(Var1((_0, _2)) = Var1((12, 34)));`
`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 `\$in` against a given pattern `\$p`. Produces `Ok(\$out)` if successful; `Err(\$in)` otherwise.