Make copying methods not transfer ownership

[oleggator]

The problem

Some copying methods transfer ownership, but that doesn't make sense and makes them difficult to use.

• Tuple::into_struct
• FunctionCtx::return_tuple
• FunctionCtx::return_tuple_mp

The solution

• Change self parameter to reference
• Rename Tuple::into_struct to Tuple::as_struct, annotate Tuple::into_struct as deprecated

Example

use std::os::raw::c_int;
use serde::{Deserialize, Serialize};
use tarantool::index::IteratorType;
use tarantool::space::Space;
use tarantool::tuple::{AsTuple, FunctionArgs, FunctionCtx, Tuple};

#[derive(Serialize, Deserialize)]
struct Args { key: u64 }
impl AsTuple for Args {}

#[derive(Serialize, Deserialize)]
struct Record { key: u64, another_key: u64, value: u64 }
impl AsTuple for Record {}

#[no_mangle]
pub extern "C" fn example_proc(ctx: FunctionCtx, args: FunctionArgs) -> c_int {
    let args: Tuple = args.into();
    let args: Args = args.as_struct().unwrap();

    let space = Space::find("some_space").unwrap();
    for tuple in space.select(IteratorType::GE, &(args.key)).unwrap() {
        // "tuple" will be passed to "return_tuple",
        // so it should not transfer ownership here
        let record: Record = tuple.as_struct().unwrap(); 
        if record.key != args.key { break; }

        // "return_tuple" may be used multiple times,
        // so it should not transfer ownership here
        ctx.return_tuple(tuple).unwrap();
    }

    0
}

[volt0]

It makes sense, but I think both options should be left. Deprecation is not required.

Please:

• remove deprecated annotation
• rollback tests and other internal usages

[oleggator]

Please notice, FunctionCtx::return_tuple(&self, tuple: &Tuple) now applies tuple as reference.
Maybe it would be better to make tuple::Tuple implement Clone trait?

[volt0]

Please notice, FunctionCtx::return_tuple(&self, tuple: &Tuple) now applies tuple as reference.

Its okay

Maybe it would be better to make tuple::Tuple implement Clone trait?

Tuple is already implements Clone