Constructors for `<:Function` types when possible, like in C++

[Mason]

Every ‘singleton’ struct can be constructed from it’s type using T.instance

julia> struct Foo end

julia> Foo.instance
Foo()

julia> typeof(sqrt).instance
sqrt (generic function with 19 methods)

julia> typeof(+).instance
+ (generic function with 206 methods)

I doubt this provides any great opportunities for optimizations though, and it’s generally not a good idea.

This sort

@nsajko

Still, even after realizing that functions are singleton types I thought that there might be a certain reason to prefer passing functions as types: the Performance of captured variables issue. I thought that passing functions as types could enable writing more concise code with closures, because let isn’t necessary for type parameters. Long story short, turns out that let is also unnecessary for variables that happen to be of singleton type.

I think you should read that section again. The boxing problem only comes into play if you rebind the captured variable.