Macro static_init_block

macro_rules! static_init_block {
    ($($body:tt)*) => { ... };
}

Run code when the program or library that holds it loads, as a C++ TVM_FFI_STATIC_INIT_BLOCK does. The body is the body of a function that returns Result<()>: it registers what the library defines, such as global functions, and stops at its first error, which ? returns. A body whose statements all end in ; returns Ok(()); one that ends in an expression returns it, a Result<()>.

use tvm_ffi::{Function, Result};

fn add_one(x: i64) -> Result<i64> {
    Ok(x + 1)
}

tvm_ffi::static_init_block! {
    Function::register_global_typed("my_ext.add_one", add_one, "Add one to an integer.")?;
}

// Registered when the program loaded.
let add_one = Function::get_global("my_ext.add_one")?;
assert_eq!(i64::try_from(add_one.call_tuple((1i64,))?)?, 2);

A block runs when its program or library loads: it adds a constructor, which the loader runs, and the first constructor runs every block of the program or library, in the order of their modules and lines. Python sees what the blocks of a library registered once it loads the library, by any means, and the library stays loaded for the process, as the registrations keep its code. An error cannot reach a caller when the library loads: it is printed, and run_static_init_blocks reports it again. Where the loader does not run the constructor, call run_static_init_blocks first. A crate that a library depends on but never names is not linked into it, nor are its blocks: name it, as use my_crate as _; does.

A block runs once per process. Every library built on the crate links its own copy of the crates it uses, so a block of a crate that several libraries link is in each of them; the first library that runs it registers what it defines, and the others skip it. A block of another version of the crate, or whose text differs, is another block, and registering what it defines again is an error. A change to the body of a function the block calls does not make another block: rebuild every library that links a crate after changing it.