Parsing a JSON payload without a top-level keyword

[weskoerber]

@ForeverZer0

Does it parse to an ArrayList(Thing)?

A top-level array is valid JSON, and if I remember correctly, Zig’s json package does parse it, though I was not specifically using parseFromSlice, which may have some additional restrictions.

Zig’s JSON parser doesn’t parse to an ArrayList(T), but you can write a wrapper that does by implementing jsonParse. See my reply on a related post.

@gonzo

Could it be you need name: []const u8 here?

[]u8 is perfectly acceptable here. []const u8 would mean the array data is immutable (i.e. name is immutable), but since parseFromSlice and it’s sibling parseFromSliceLeaky allocate memory for the parsed result there aren’t any concerns about the constness of the data (there may be in your application, but from an API level there aren’t).

---

@zgasma

I tried:

const Thing = struct {
    name: []u8,
};

const Things = []Thing;

but that gives me:

error: UnexpectedToken
/home/me/.local/lib/std/json/static.zig:334:53: 0x17538a5 in innerParse__anon_40140 (app)
            if (.object_begin != try source.next()) return error.UnexpectedToken;

Anyways, I’m not sure why you’re getting an error in the first place. I suspect it’s some other issue related to your input or type definition, as the contrived example you provided works on my machine (tested with Zig versions 0.12.0, 0.13.0, 0.14.0, and 0.15.0-dev.621+a63f7875f):

const std = @import("std");

const Thing = struct {
    name: []u8,
};

const Things = []Thing;

pub fn main() !void {
    const str =
        \\[{"name": "thing1"}, {"name": "thing2"}]
    ;

    const things = try std.json.parseFromSlice(Things, std.heap.page_allocator, str, .{});

    for (things.value) |thing| {
        std.debug.print("{s}\n", .{thing.name});
    }
}

This prints

thing1
thing2

to my console.