Performance wise it makes no difference. The JIT will produce the same code
for all three:
foo1(x::Real, y::Real) = x + y
foo2{ T<: Real}(x::T, y::T) = x + y
foo3{T <: Real, S <: Real}(x::T, y::S) = x + y
You can verify it by running @code_native on all of them. They will all
result in the same machine code for the same input types.
@code_native foo1(1, 1)
.text
Filename: none
Source line: 1
push RBP
mov RBP, RSP
Source line: 1
add RCX, RDX
mov RAX, RCX
pop RBP
ret
The one difference is that foo2 requires both x and y to be of the same
type:
foo2(1, 1.0)
`foo2` has no method matching foo2(::Int64, ::Float64)
You can mix and match Real types with foo1 and foo3.
On Tuesday, August 19, 2014 9:30:42 PM UTC+3, Spencer Lyon wrote:
>
> Suppose I am defining a function that operates on any two real numbers.
> Which of the following ways of specifying types is preferred (in terms of
> idomatic Julia and performance considerations) and why?
>
> ```julia
>
> function foo1(x::Real, y::Real) = ...
>
> function foo2{ T<: Real}(x::T, y::T) = ...
>
> function foo3{T <: Real, S <: Real}(x::T, y::S) = ...
> ```
>
>
