Help me understand some of `io.zig` in the standard library

Explain
1

Ok, new to Zig, maybee too soon for me to be skimming the standard library code, but there isn’t much documentation. (Not a complaint - I know it is a new language, and frankly, the code almost looks understandable to me at this point, which is sort of amazing to me).

So, fn GenericWriter defines a structure in it’s body, and returns it (which is cool). There are a few functions defined in the structure, such as writeStructEndian that have bodies like: return @errorCast(self.any().writeStructEndian(value, endian));.

So, the any function in the struct, also returns an anonymous struct having fields: .context and .writeFn … so here’s my confusion: in following self.any(), I’m assuming that writeStructureEndian is then called on the anonymous structure? How does that work? The anonymous structure doesn’t define that function and Zig doesn’t have inheritance?

2

The anyonymous struct literal creates an instance with the type of the return type of the any function and the return type has the writeStructureEndian method.

3

So, the anonymous constructor serves to fill in default values for an AnyWriter struct (which does have a writeStructureEndian` method)?

If so, I guess I wasn’t catching that the anon struct was used like that.

4

In Zig every value has a type, anonymous structs literals just allow you to have that type be inferred based on the type of the result location.

Zig doesn’t have constructors.

No default values, but it creates a struct instance of type AnyWriter with specific values, yes.

AnyWriter is declared as:

pub const AnyWriter = @import("io/Writer.zig");

And this imports the #src/std/io/Writer.zig struct.

related:

4 Likes
5

FWIW, I think it’s a little hard to follow what’s going on with this when browsing through these types via the standard library reference docs.

6

I always read the std source directly instead.