The function `get`

in `dict.jl`

has the following signature:

```
function get(default::Callable, h::Dict{K,V}, key) where V where K
```

I am wondering: what does `Callable`

mean? Perhaps `Union{Function,Type}`

? Also, does it specialize? It seems like `get`

is a function that ought to specialize for better performance. In other words, why is this not written as:

```
function get(default::T, h::Dict{K,V}, key) where T where V where K
```

(I am rewriting the sorted container code in DataStructures.jl and would like to follow an appropriate pattern for `get`

and `get!`

)