Macro assert_matches2::assert_let

macro_rules! assert_let {
    ($pat:pat = $e:expr) => { ... };
    ($pat:pat = $e:expr, $($arg:tt)*) => { ... };
}

Alternative form of assert_matches! where the pattern comes first.

If the assertion fails, the expression after the = is debug-printed as part of the panic message.

Example

use assert_matches2::assert_let;
use serde_json::{json, Value as JsonValue};

let val = json!({ "field": [1, 2, 3] });
assert_let!(JsonValue::Object(obj) = val);
assert_eq!(obj.len(), 1);
assert_let!(Some((field_name, JsonValue::Array(arr))) = obj.into_iter().next());
assert_eq!(field_name, "field");
assert_eq!(arr, [1, 2, 3]);