Compile Time HashMap in Zig

Question

Take for example the Rust library lazy_static's example:

use lazy_static::lazy_static;
use std::collections::HashMap;

lazy_static! {
    static ref HASHMAP: HashMap<u32, &'static str> = {
        let mut m = HashMap::new();
        m.insert(0, "foo");
        m.insert(1, "bar");
        m.insert(2, "baz");
        m
    };
    static ref COUNT: usize = HASHMAP.len();
    static ref NUMBER: u32 = times_two(21);
}

How might this be done in Zig?

I have tried this which is the only thing that makes sense to me:

const std = @import("std");

pub fn main() void {
    comptime var h = std.StringHashMap(i32).init(std.testing.allocator);
    h.put("hi", 5) catch {};
    std.debug.print("{}", .{h});
}

but this segfaults.

Is it even possible to do this in Zig?

In the future, it will eventually be possible to create a normal StringHashMap at comptime using a comptime allocator, but in the current version of zig this would be extremely slow and crashes the compiler. — pfg
– pfg, Commented Jul 14, 2022 at 4:50

Mai Lapyst · Accepted Answer · 2024-11-26 15:58:47Z

2

Since zig 0.13.0

With zig 0.13.0, the previously known std.ComptimeStringMap was renamed in commit 8af59d1 to std.StaticStringMap, and now lives here in the standard library.

Until zig 0.12.1

It seems (thanks to this Reddit post) that this is implemented in the standard library

and can be used via std.ComptimeStringMap

This however does not seem to support any dynamic insertion as there is no insert method.

edited Nov 26, 2024 at 15:58

Mai Lapyst

52 silver badges4 bronze badges

answered Jul 2, 2022 at 0:57

CircArgs

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