# Overload call to do multiplication on numbers?

I really like the 2x syntax, and get tired of writing stars.

edit: actual example…

``````function (x::Float64)(y)
x*y
end
a = 2.0
a(2+2)
``````

That looks like a hilariously bad idea, but I can’t find any actual problems with this. Anything I missed?

This already works without that definition though:

``````julia> 2.0pi
6.283185307179586

julia> 2.0(2+2)
8.0

julia> 2.0sin(pi)
2.4492935982947064e-16
``````
2 Likes

Sorry about that, I changed my example but didn’t test What didn’t work without the definition was:

``````a = 2.0
a(2+2)
``````
``````julia> pi(2+2)
ERROR: MethodError: objects of type Irrational{:π} are not callable

julia> a = 2
2

julia> a(2+2)
ERROR: MethodError: objects of type Int64 are not callable
``````

But I get what you mean.

It looks like function call syntax, so for the examples above I would expect to call a function `pi` and `a` respectively.

Sorry again, I edited my second post (I should really wait to be on a computer before replying…)

My motivating example was writing `sin(2pi(x+y))` by accident and wondering if that could work.

It’s definitely doable, but it seems a bit dangerous. I wouldn’t want to have `sin = 666` somewhere and then write `sin(x + y)` later, thinking that I’m calling the `sin` function but actually just be multiplying `x + y` by the number of the beast.

6 Likes

I really like that in Mathematica `a b` Lowers to `a*b`. This would probably be horribly invasive and dangerous to implement in Julia but man would I love to be able to write `sin(2pi (x+y))` and have the space between `2pi` and `(x+y)` be understood as multiplication.

1 Like

That’s fair enough, this feature, while very cool, is also fairly dangerous. For those interested:

``````function build_subtypes(T)
concretes = [t for t in subtypes(T) if isempty(subtypes(t))]
abstracts = [t for t in subtypes(T) if !isempty(subtypes(t))]
types = []
append!(types, concretes)
for t in abstracts
append!(types, build_subtypes(t))
end
types
end

for T in build_subtypes(Number)
@eval begin
function (x::\$T)(y)
x*y
end
end
end
``````
1 Like

Space is already used as a separator in matrices, so `sin.([2pi (x+y)])` would be ambiguous…

Right, I had a feeling there was something that would straight up clash with spaces as multiplication. How could I forget row vectors and matrices!