Make struct definition return the defined type

Internals & Design
1

Currently a struct definition returns nothing:

julia> x = struct Foo end

julia> x === nothing
true

How about it returning the defined type instead?

julia> x = struct Foo end

julia> x === Foo
true

Why would this behaviour be useful? It would make the following pattern to “redefine types” more convenient:


Foo = struct Foo1
    field1
end

function doit(foo::Foo)
    foo.field1 + foo.field2
end

Now we can simply edit the above without restarting julia and it will work:

Foo = struct Foo2{T <: Number}
    field1::T
    field2::T
end

function doit(foo::Foo)
    foo.field1 + foo.field2
end

Or even

Foo = @eval struct $(gensym())
           field1
           field2
       end
1 Like
2

I don’t think we should introduce a language future just to work around the issues addressed by

2 Likes
3

I agree that one should not introduce language features just to hack around other limitations. However this one is also natural and consistent. For instance function definitions return the definied function.

4

It’s actually pretty reasonable for a type definition to return the type that’s defined though. The main reason we don’t do that is because printing the type in the REPL after it’s defined is a bit annoying. Returning the type would be more lispy.

1 Like