Macro hopper_interface 

macro_rules! hopper_interface {
    (
        $(#[$attr:meta])*
        pub struct $name:ident, disc = $disc:literal, version = $ver:literal
        {
            $(
                $(#[$field_attr:meta])*
                $field:ident : $fty:ty = $fsize:literal
            ),+ $(,)?
        }
    ) => { ... };
}

Declare a cross-program interface view.

Generates a read-only overlay struct for reading accounts owned by another program without any crate dependency. The interface is pinned by LAYOUT_ID – the same deterministic SHA-256 fingerprint used by hopper_layout!. If the originating program changes its layout, the fingerprint will differ and load_foreign() will reject the account at runtime.

The generated struct includes:

• #[repr(C)] zero-copy overlay with alignment-1 guarantee
• Deterministic LAYOUT_ID matching the originating layout
• load_foreign(account, expected_owner) for Tier-2 cross-program reads
• load_foreign_multi(account, owners) for multi-owner scenarios
• load_with_profile(account, TrustProfile) for configurable trust
• Compile-time size and alignment assertions

Example

Program A defines a Vault:

hopper_layout! {
    pub struct Vault, disc = 1, version = 1 {
        authority: TypedAddress<Authority> = 32,
        balance:   WireU64                = 8,
        bump:      u8                     = 1,
    }
}

Program B reads it without importing Program A:

hopper_interface! {
    /// Read-only view of Program A's Vault.
    pub struct VaultView, disc = 1, version = 1 {
        authority: TypedAddress<Authority> = 32,
        balance:   WireU64                = 8,
        bump:      u8                     = 1,
    }
}

let verified = VaultView::load_foreign(vault_account, &PROGRAM_A_ID)?;
let balance = verified.get().balance.get();

If the fields match Program A’s Vault exactly, the LAYOUT_IDs will be identical and load_foreign succeeds. Any structural divergence produces a different hash and the load fails.