print-type-sizes-vec.rs

#![feature(allocator_api)]

use std::alloc::Allocator;
use std::alloc::Global;
use std::marker::PhantomData;

// Basicaly a Vec.
pub struct V<T, A: Allocator = Global> {
    pub buf: Rv<T, A>,
    pub len: usize,
}

// Basically a RawVec.
pub struct Rv<T, A: Allocator = Global> {
    pub ptr: Unique<T>,
    pub cap: usize,
    pub alloc: A,
}

// Basically a Unique.
pub struct Unique<T: ?Sized> {
    pub pointer: *const T,
    pub _marker: PhantomData<T>,
}

fn main() {
    // Builtin.

    //RUSTFLAGS="$RUSTFLAGS -Zprint-type-sizes" cargo +nightly build --release

    //print-type-size type: `std::vec::Vec<i32>`: 24 bytes, alignment: 8 bytes
    //print-type-size     field `.buf`: 16 bytes
    //print-type-size     field `.len`: 8 bytes
    //print-type-size type: `alloc::raw_vec::RawVec<i32>`: 16 bytes, alignment: 8 bytes
    //print-type-size     field `.alloc`: 0 bytes
    //print-type-size     field `.ptr`: 8 bytes
    //print-type-size     field `.cap`: 8 bytes

    //RUSTFLAGS="$RUSTFLAGS --emit llvm-ir" cargo +nightly build --release
    //cat target/release/deps/type_sizes-dbd3f07f95882e7a.ll | rustfilt | less

    //%"alloc::vec::Vec<i32>" = type { { i32*, i64 }, i64 }
    let xs = vec![1, 2, 3];
    println!("{:?} takes up {} bytes", xs, std::mem::size_of_val(&xs));

    // Homespun.
    let ys = V {
        buf: Rv {
            ptr: Unique {
                pointer: std::mem::align_of::<i32>() as *mut i32,
                _marker: PhantomData,
            },
            cap: 0,
            alloc: Global,
        },
        len: 0,
    };

    //print-type-size type: `V<i32>`: 24 bytes, alignment: 8 bytes
    //print-type-size     field `.buf`: 16 bytes
    //print-type-size     field `.len`: 8 bytes
    // ...
    //print-type-size type: `Rv<i32>`: 16 bytes, alignment: 8 bytes
    //print-type-size     field `.alloc`: 0 bytes
    //print-type-size     field `.ptr`: 8 bytes
    //print-type-size     field `.cap`: 8 bytes

    // !499 = !DICompositeType(tag: DW_TAG_structure_type, name: "V<i32, alloc::alloc::Global>", scope:
    // !500, file: !2, size: 192, align: 64, elements: !501, templateParams: !320, identifier: "a134b15c57d7976d79d922cfe8e48ad2")
    // ...
    //
    // !503 = !DICompositeType(tag: DW_TAG_structure_type, name: "Rv<i32, alloc::alloc::Global>", scope:
    // !500, file: !2, size: 128, align: 64, elements: !504, templateParams: !320, identifier: "5377eda6ce5cb55c8f9ffedb4de51a6d")
    println!("V takes up {} bytes", std::mem::size_of_val(&ys));
}