Variable const error and immutable proposal.

[EchoPouet]

Hello,

I would like convert a simple Zig code to test C3 features, the code:

import std::io;

fn int main()
{
    char[8] some_primes = {1, 3, 5, 7, 11, 13, 17, 19};

    some_primes[0] = 2;

    const char FIRST = some_primes[0];

    const char FOURTH = some_primes[3];

    const usz LENGHT = some_primes.len;

    io::printfn("First: %d, Fourth: %d, Length: %d", FIRST, FOURTH, LENGHT);

    return 0;
}

And I have this error mesage:

 6: 
 7:     some_primes[0] = 2;
 8: 
 9:     const char FIRST = some_primes[0];
                           ^^^^^^^^^^^^^^
(003_arrays.c3:9:24) Error: The expression must be a constant value.

 8: 
 9:     const char FIRST = some_primes[0];
10: 
11:     const char FOURTH = some_primes[3];
                            ^^^^^^^^^^^^^^
(003_arrays.c3:11:25) Error: The expression must be a constant value.

"const" indicate that the variable can't be re-assigned and it's the case with my example code. Also I found Constant expressions and I doesn't understand why it can't work because FIRST and FOURTH take integer value. I'd agree if these variables were pointers or references, but it's not the case.

After explanation in Discord I made a proposal.

Like some others languages (Nim, Rust ...) I propose "let" statement to declare symbols are single assignment variables: After the initialization their value cannot change.

import std::io;

fn int main()
{
    char[8] some_primes = {1, 3, 5, 7, 11, 13, 17, 19};

    some_primes[0] = 2;

    let char first = some_primes[0]; // OK

    let char fourth = some_primes[3];

    first = 8; // Error, let variable can't be re-assigned

    const usz LENGHT = some_primes.len;

    io::printfn("First: %d, Fourth: %d, Length: %d", first, fourth, LENGHT);

    return 0;
}

Thanks.