Golang struct inheritance not working as intended?

Golang doesn't provide the typical notion of inheritance. What you are accomplishing here is embedding.

It does not give the outer struct the fields of the inner struct but instead allows the outer struct to access the fields of the inner struct.

In order to create the outer struct Something you need to give its fields which include the inner struct Base

In your case:

Something{Base: Base{a: "letter a"}, c: "letter c"}

You have to actually instantiate the embedded struct as well. Just so you know this isn't inheritance technically, no such feature exists in Go. It's called embedding. It just hoists fields and methods from the embedded type to the embeddors scope. So anyway, the composite literal instantiation you're trying to do would look like this;

f(Something{
    Base: Base{a: "a", b: "b"},
    c:    "c",
})

You need to explicitly create Base field like that

f(Something{
    Base: Base{a: "letter a"},
    c:    "letter c",
})

Go has no inheritance, it is just composition.