Declarative macros with non-const values

1

I want to write a macro that return a [u8; some size] something akin to vec!.

macro_rules! buf{
    ($a:expr)=>{
        {
            [0u8; $a]
        }
    }
}

This works but I need to pass a const to buf!(). How can I change it to take a variable? For instance I want to use it as follows:


let len = get_some_size();
let buf = buf!(len);

Is this possible? Thanks in advance.

2

An array, by definition, has a size set at compile time, so you cannot use a variable to pick the size. This is true whether or not macros are involved.

1 Like
3

To expand on that, from the docs for the primitive type array:

A fixed-size array, denoted [T; N], for the element type, T, and the non-negative compile-time constant size, N.

Perhaps you want to use a vector instead?

let len = get_some_size();
let buf = vec![0u8; len];
5

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