Functions with 2 generic types

New to Julia
1

I’m trying to have a function with 2 inputs with different generic types, so I wrote the below:

function mysum(x::T, y::V) where {T, V}
       x+y
end

It worked fine with number, but it accept also Bool inputs, how can I avoid this, and tell ensure the function accept numbers only!

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2

You can add type constraints to your generic types.

function mysum(x::T, y::V) where {T<:Number, V<:Number}
       x+y
end

But in this case the easiest way to write this would simply be

function mysum(x::Number, y::Number)
       x+y
end
3

both solution still accept boolian s input :frowning:

4

Oh that’s true, since Boolean<:Number in Julia

julia> 1 + true
2

julia> 1 + false
1

julia> 2.0 * true
2.0

julia> 2.0 * false
0.0

So this is in some sense what you want.

5

If you really don’t want booleans in your function, you could define a method

mySum(x::Bool, y:: Number) = error("Needs non-booleans!") 
mySum(x::Number, y::Bool) = error("Needs non-booleans!")

All other numbers will work then.

6

Actually what I need I is to get an error, not Zero, if any of the 2 inputs is not a number (I mean real number that can be manipulated)

7

Can you say exactly what sort of numbers you want, then? Should complex numbers be accepted? Booleans are numbers, so why not them? Can you specify?

8

I mean by numbers any thing from 0123456789 regardless Int, Float,UInt,…

9

If I want to do this for more than a function it will be a headache; thanks for the try.

10

But Bool belongs to that set. Could you give a definition of the numbers you want, or is it “anything except Bool”?

11

A quick (not so elegant) fix, but it works:

julia> function mysum(x::T, y::V) where {T<:Union{Signed, Unsigned, AbstractFloat, AbstractIrrational, Rational}} where {V<:Union{Signed, Unsigned, AbstractFloat, AbstractIrrational, Rational}}
         x + y
       end
mysum (generic function with 1 method)

julia> mysum(2,3)
5

julia> mysum(2,3.2)
5.2

julia> mysum(2,true)
ERROR: MethodError: no method matching mysum(::Int64, ::Bool)
Closest candidates are:
  mysum(::T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, ::V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}) where {V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}} at REPL[13]:2
Stacktrace:
 [1] top-level scope at none:0

Edit: It doesn’t cover all cases though!

12

I think this one works:

julia> const U = Union{Signed, Unsigned, AbstractFloat, AbstractIrrational, Rational}
Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}

julia> function mysum(x::T, y::V) where {T<:U,V<:U}
         x + y
       end
mysum (generic function with 1 method)

julia> mysum(2,3)
5

julia> mysum(2,3.2)
5.2

julia> mysum(2.2,3.2)
5.4

julia> mysum(2.2,3)
5.2

julia> mysum(2.2,true)
ERROR: MethodError: no method matching mysum(::Float64, ::Bool)
Closest candidates are:
  mysum(::T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, ::V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}) where {T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}} at REPL[2]:2
Stacktrace:
 [1] top-level scope at none:0

julia> mysum(true,2.2)
ERROR: MethodError: no method matching mysum(::Bool, ::Float64)
Closest candidates are:
  mysum(::T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, ::V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}) where {T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}} at REPL[2]:2
Stacktrace:
 [1] top-level scope at none:0

You can check methods:

julia> methods(mysum)
# 1 method for generic function "mysum":
[1] mysum(x::T, y::V) where {T<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}, V<:Union{AbstractIrrational, AbstractFloat, Signed, Unsigned, Rational}} in Main at REPL[2]:2
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