Are "temporaries" always const?

Explain
1

I can take the address of an expression without assigning it to a variable first, but apparently it is const:

const std = @import("std");

fn f1() i32 {
    return 42;
}

fn f2(p: *const i32) void {
    std.debug.print("{}\n", .{p.*});
}

fn f3(p: *i32) void {
    p.* += 1;
    std.debug.print("{}\n", .{p.*});
}

pub fn main() void {
    f2(&f1()); // works
    f3(&f1()); // error: expected type '*i32', found '*const i32'
    f3(@constCast(&f1())); // this makes it work?
}

Is there a reason why it has to be immutable? As far as I understand it’s just a temporary value stored on the stack.

Is it safe to just constCast it?

2

Temporaries are always const and no its not safe to constCast it. Zig requires mutable references to always point to a location which clearly implies that it is backed by some sort of storage.