The type of a standard Julia function f is typeof(f), which is a singleton. julia> function f end f (generic function with 0 methods) julia> typeof(f) typeof(f) (singleton type of function f, subtype of Function) But it is not possible to recover the type’s sole instance with a constructor. juli…

[image] brainandforce: Is there a way to do this that doesn’t depend on using internals of the function type? If not, is there some reason why constructing a function from its type is a bad idea? No, because it might not exist! For example, Returns is a Function, but this doesn’t work: jul…

Not sure what you need this for, but here you go :slight_smile: julia> function f end f (generic function with 0 methods) julia> typeof(f).instance f (generic function with 0 methods) julia> typeof(f).instance() ERROR: MethodError: no method matching f() The function `f` exists, but no method is …

Thanks - I was trying to build a data structure that represented the lazy application of a function, but I realized that it wouldn’t make much sense to do it the way I originally envisioned. At this point I’m more so interested out of curiosity. I’m left with two questions now: Is there a way to …

[image] brainandforce: julia> typeof(f)() ERROR: MethodError: no method matching typeof(f)() The type `typeof(f)` exists, but no method is defined for this combination of argument types when trying to construct it. Stacktrace: [1] top-level scope @ REPL[6]:1 Is there any way to do this? I…

The OP started out by talking about [image] brainandforce: standard Julia function which Returns is not; Returns is a struct that subtypes Function. So, I was wondering if there is an answer to the questions [image] brainandforce: Is there a way to do this that doesn’t depend on using …

What’s a “standard Julia function?” I’m not sure I know. What about this Returns? julia> f = Returns(nothing) Returns{Nothing}(nothing) julia> typeof(f).instance # it works! Returns{Nothing}(nothing) Why should that work? Or what about a closure? julia> printer(x) = ()->println(x) printer (ge…

The reason I asked this was in the case of something like struct Foo{F<:Function} end you could not work with the stored function by instantiating it like a normal concrete type: function bar(baz, ::Foo{F}) where F f = F() return f(baz) end Instead you’d have to do something along the li…

julia> sizeof(sin) 0 julia> sizeof(Returns(nothing)) 0 julia> sizeof(Returns(3)) 8 In most cases where the function is a singleton that can be retrieved from .instance, it also has sizeof(F) == 0. So while it does take up a “field” in the struct, it does not require any memory. In other words, th…

I was defining “standard Julia functions” as those defined with the function keyword (or the shortened, math-like syntax) in the top-level scope (not an inner function, not a closure, not an anonymous function). But even that definition is more nuanced than I originally thought because it includes c…

[image] mbauman: What’s a “standard Julia function?” I’m not sure I know. Probably they mean a global function that you define with function foo(...) .... or equivalent, which is a singleton subtype of Function. See also this thread: How to get a function instance from a function type? - #2 …

Creating the instance of a function type

General Usage

raminammour November 6, 2024, 8:42pm 4

This thread seems to have some clues, and I would heed the advice rather than relying on internals…

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Creating the instance of a function type

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