sx/examples/1217-ffi-09-extern-result-chain.sx

// Phase 0 baseline (PLAN-FFI.md step 0.9): FFI result chains. The
// shapes that real sx code uses for opaque C handles (MTLBuffer*,
// AAssetManager*, file pointers, ...) — passing a C-returned
// pointer into another C call, stashing it in a struct field,
// pushing into a `List(*void)`, and iterating that list to feed each
// handle back through C.
//
// No new ABI shape — pointer-in, pointer-out. The lemma locked in:
// handle-shaped flows survive sx's struct-field assignment, List
// storage, and iteration-then-call cycles.

#import "modules/std.sx";

#import c {
    #include "1217-ffi-09-extern-result-chain.h";
    #source "1217-ffi-09-extern-result-chain.c";
};

// Struct field hosts an FFI-returned handle.
Counter :: struct {
    handle: *void = null;
    label: string;
}

main :: () -> i32 {
    // ── 1. Chain: make → bump → peek ───────────────────────────────
    a := ffi_chain_make(100);
    print("peek after make    = {}\n", ffi_chain_peek(a));
    print("bump(+5)           = {}\n", ffi_chain_bump(a, 5));
    print("bump(+3)           = {}\n", ffi_chain_bump(a, 3));
    print("peek after bumps   = {}\n", ffi_chain_peek(a));

    // ── 2. Stash handle in a struct field, use through `.handle` ──
    c : Counter = .{ handle = ffi_chain_make(50), label = "ctr-a" };
    print("ctr label          = {}\n", c.label);
    print("ctr peek           = {}\n", ffi_chain_peek(c.handle));
    ffi_chain_bump(c.handle, 7);
    print("ctr after bump     = {}\n", ffi_chain_peek(c.handle));

    // ── 3. Push handles into a List, iterate, feed back to C ──────
    handles : List(*void) = .{};
    i : i32 = 0;
    while i < 3 {
        h := ffi_chain_make(i * 10);
        handles.append(h);
        i += 1;
    }

    j : i64 = 0;
    while j < handles.len {
        h := handles.items[j];
        v := ffi_chain_peek(h);
        print("list[{}] peek      = {}\n", j, v);
        j += 1;
    }

    // Iterate again, bump each, observe the cumulative effect.
    j = 0;
    while j < handles.len {
        ffi_chain_bump(handles.items[j], 1);
        j += 1;
    }
    j = 0;
    while j < handles.len {
        print("list[{}] after bump= {}\n", j, ffi_chain_peek(handles.items[j]));
        j += 1;
    }

    // ── Cleanup ─────────────────────────────────────────────────────
    ffi_chain_dispose(a);
    ffi_chain_dispose(c.handle);
    j = 0;
    while j < handles.len {
        ffi_chain_dispose(handles.items[j]);
        j += 1;
    }

    0
}