You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: block_ptr.rs
    path of file: ./repos/c2rust/c2rust-refactor/runtime/src
    
    the code of the file until where you have to start completion: use std::mem;
use std::ptr::{self, NonNull};
use libc;

use util::Nullable;


/// A pointer to the start of a `malloc`'ed block.  Provides rudimentary bounds checking based on
/
    
    pub fn alloc(len: usize) -> CBlockPtr<T> {
        if len == 0 {
            return Self::empty();
        }

        let size = mem::size_of::<T>();
        if size == 0 {
            CBlockPtr(NonNull::dangling().as_ptr())
        } else {
            let byte_len = len.checked_mul(size)
                .unwrap_or_else(|| panic!("overflow when allocating {} elements of size {}",
                                          len, size));
            unsafe {
                let ptr = libc::malloc(byte_len as libc::size_t);
                assert!(!ptr.is_null(), "malloc of {} bytes failed", byte_len);
                CBlockPtr(ptr as *mut T)
            }
        }
    }