In terms of type stability (
http://docs.julialang.org/en/release-0.4/manual/performance-tips/#avoid-changing-the-type-of-a-variable
), the latter is better:
f1(x::Int, y::Union{Void,Dict}) = y==nothing ? Dict() : y
@code_warntype f1(42, nothing) # shows ...end::UNION{DICT{ANY,ANY},VOID};
type unstable!
@code_warntype f1(42, Dict()) # shows ...end::Dict{Any,Any}
compare this to
f2(x::Int, y::Dict=Dict()) = y
@code_warntype f2(42) # shows ...end::Dict{Any,Any}; type stable
@code_warntype f2(42, Dict()) # shows ... end::Dict{Any,Any}
Whether you write f(x::Int, y=Dict()) or f(x::Int, y::Dict=Dict()) is a
separate issue, about which Tamas and Tom made good suggestions.
On Thursday, May 5, 2016 at 1:58:42 PM UTC+2, Tom Breloff wrote:
>
> Just to extend Tamas's note... Another reason you may add the type
> annotation is to ensure your code errors when you pass it types that are
> not valid (but may compile and dispatch without issue).
>
> On Thursday, May 5, 2016, Tamas Papp <[email protected] <javascript:>>
> wrote:
>
>> Hard to say without the context, but since in this case the only purpose
>> of a `nothing` seems to be to initialize with a default value, I would
>> go with y=Dict(), which does it directly.
>>
>> (Note that unless you are dispatching on them, your type declarations
>> are probably unnecessary, they won't make your code faster.)
>>
>> On Thu, May 05 2016, FANG Colin wrote:
>>
>> > For example,
>> >
>> > function f(x::Int; y::Union{Void, Dict})
>> > z = y == nothing ? Dict() : y
>> > ...
>> > end
>> >
>> >
>> > Or
>> >
>> > function f(x::Int; y::Dict=Dict())
>> > ...
>> > end
>> >
>> > Which one should I use?
>>
>
