Declare const or var depending on comptime const

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1

I need ideally a (global) const to be var depending on a comptime boolean.
Is that possible in 1 declaration?

pub const we_can_change: bool = false;

pub const value: i32 = 42; // if we_can_change is false
pub var value: i32 = 42; // if we_can_change is true
2

The one way I can think of right now would be something like

const std = @import("std");

// Compile error, "cannot assign to constant"
// const we_can_change = false;

// Runs just fine!
const we_can_change = true;

pub const wrapper = if (we_can_change) struct {
    pub var value: i32 = 42;
} else struct {
    pub const value: i32 = 42;
};

// Skipping the wrapper by using a pointer
// is another option
// pub const value = &wrapper.value;

pub fn main() !void {
    wrapper.value = 12;

    std.debug.print("{d}\n", .{wrapper.value});
}

Edit: This of course also works if you define wrapper inside main instead, though that would probably defeat the purpose.

Edit 2: A more direct way to go the pointer route, the sacrifice being a second declaration:

var backing: i32 = 42;
pub const value: if (we_can_change) *i32 else *const i32 = &backing;
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3

good ideas. fooling around with it now.

But if we go the pointer way, we need allocations right?
Edit: in my case it is more complicated. mutable type = 4 fields in a struct, unmutable type is a hard constant.

4

@Fitti’s code works verbatim, you can point to global memory.

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