Do struct field initializations occur in well defined order?

kj4tmp · July 28, 2024, 4:57am

Are the fields in the following struct guaranteed to initialize in a specific order (will the reader always read dest_mac, src_mac, then ether_type?

const ethernet_header = telegram.EthernetHeader{
            .dest_mac = try reader.readInt(u48, big),
            .src_mac = try reader.readInt(u48, big),
            .ether_type = try reader.readInt(u16, big),
        };

kj4tmp · July 28, 2024, 5:44am

this issue infers that it is well defined.

As far as I can tell, it occurs left-to-right.

github.com/ziglang/zig

zig fmt: reorder struct initialization to be consistent with the struct definition

opened 10:39AM - 11 Feb 24 UTC

closed 04:25AM - 12 Feb 24 UTC

anyputer

proposal zig fmt

I always reorder struct field initialization order to be consistent with the ord…er of the fields in the type. It would be nice if zig fmt could automatically do this so I don't have to. For instance: ```zig const Foo = struct { y: u8, a: u8, x: u8 }; const foo = Foo { .a = 42, .x = 69, .y = 32 }; ``` would get formatted as: ```zig const Foo = struct { y: u8, a: u8, x: u8 }; const foo = Foo { .y = 32, .a = 42, .x = 69 }; ```

dimdin · July 28, 2024, 6:57am

It initializes with the initialization order. But it is not mentioned in the language reference.

A way around this is to have a fn read(reader) !EthernetHeader method to read in the correct order and construct your header, that works even if zig language specification change.