Macro const_panic::inline_macro

macro_rules! inline_macro {
    ($(($($args : tt) *)), * $(,) ? ; ($($params : tt) *) => $($code : tt) *) => { ... };
}

This is supported on crate feature non_basic only.

Helper macro for defining and using a macro_rules! macro inline.

The reason this was defined is to work around a limitation in stable const-eval, where you can’t call methods on generic types.

Example

Implementing panic formatting for a generic struct.

use const_panic::{ArrayString, FmtArg, impl_panicfmt, inline_macro};

// Debug formatting
assert_eq!(
    ArrayString::<99>::from_panicvals(
        &Foo(10, 20).to_panicvals(FmtArg::DEBUG)
    ).unwrap(),
    "Foo(10, 20)"
);

// Alternate-Debug formatting
assert_eq!(
    ArrayString::<99>::from_panicvals(
        &Foo(false, true).to_panicvals(FmtArg::ALT_DEBUG)
    ).unwrap(),
    concat!(
        "Foo(\n",
        "    false,\n",
        "    true,\n",
        ")",
    ),
);

// Display formatting
assert_eq!(
    ArrayString::<99>::from_panicvals(
        &Foo("hmm", "what?").to_panicvals(FmtArg::DISPLAY)
    ).unwrap(),
    "Foo(hmm, what?)"
);




struct Foo<T>(T, T);

// Because of limitations of stable const evaluation,
// you have to use macros to implement panic formatting
// for more than one concrete type (ignoring lifetimes).
//
// This macro implements panic formatting for
// - `Foo<bool>`
// - `Foo<u8>`
// - `Foo<&str>`
inline_macro! {
    (bool),
    (u8),
    // Types with lifetimes must either elide the lifetime, use `'_` or `'static`.
    (&str);

    ($T:ty) =>
    impl_panicfmt!{
        impl Foo<$T>;
        struct Foo($T, $T)
    }
}