Why @typeInfo(struct).Struct.decls is always empty?

Help
1

I’m trying to access struct declarations:

const Type = struct {
    const decl1 = void;
    const decl2 = void;
    const decl3 = void;
};

pub fn printOutDecls(comptime T: type) void {
    std.log.debug("{any}", .{@typeInfo(T).Struct.decls});
}

pub fn main() !void {
    printOutDecls(Type);
}

But unfortunately, I always get an empty list:

debug: {  }

Any ideas why is that?

Just in case, according to docs, decls is a slice of Declarations ([]const Declaration), where Declaration is a struct with a name literal (const Declaration = { name: []const u8 }).

2

Those aren’t declarations, those are privately namespaced type alias definitions. Not sure if there’s an easy way to print them out, though.

These would be public declarations:

const std = @import("std");

const Type = struct {
    pub fn decl1() void {}
    pub fn decl2() void {}
    pub fn decl3() void {}
};

fn printOutDecls(comptime T: type) void {
    for (@typeInfo(T).Struct.decls) |decl| {
        std.debug.print("{s}\n", .{decl.name});
    }
}

pub fn main() void {
    printOutDecls(Type);
}
3

Em… I’m a bit confused :slight_smile:

image

There isn’t much about what declaration really is but from the example above I thought that anything other than a field becomes a “declaration”. Seems I was making a wrong assumption.

Anyway, can I have access to those “privately namespaced type alias definitions” through the type information?

4

Oh, yeah, my bad :sweat_smile:

Here, just make em public:

const std = @import("std");

const Type = struct {
    pub const decl1 = void;
    pub const decl2 = void;
    pub const decl3 = void;
};

fn printOutDecls(comptime T: type) void {
    for (@typeInfo(T).Struct.decls) |decl| {
        std.debug.print("{s}\n", .{decl.name});
    }
}

pub fn main() void {
    printOutDecls(Type);
}
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