FWIW this is should work fine on master and the solution is likely to be
backported to the next 0.5.x version
(https://github.com/JuliaLang/julia/pull/19245).
On Sunday, November 13, 2016 at 10:16:20 AM UTC-6, bogumil....@gmail.com
wrote:
>
> Consider the following two functions:
>
> function f1(t, a)
> [t(x) for x in a]
> end
>
> function f2(t, a)
> Dict((x, t(x)) for x in a)
> end
>
> When I run @code_warntype on them I get:
>
> julia> @code_warntype f1(sin, [1.0, 2.0])
> Variables:
> #self#::#f1
> t::Base.#sin
> a::Array{Float64,1}
>
> Body:
> begin
> return $(Expr(:invoke, LambdaInfo for
> collect(::Base.Generator{Array{Float64,1},Base.#sin}), :(Base.collect),
> :($(Expr(:new, Base.Generator{Array{Float64,1},Base.#sin}, :(t), :(a))))))
> end::Array{Float64,1}
>
> julia> @code_warntype f2(sin, [1.0, 2.0])
> Variables:
> #self#::#f2
> t::Base.#sin
> a::Array{Float64,1}
> #1::##1#2{Base.#sin}
>
> Body:
> begin
> #1::##1#2{Base.#sin} = $(Expr(:new, ##1#2{Base.#sin}, :(t)))
> SSAValue(0) = #1::##1#2{Base.#sin}
> SSAValue(1) = $(Expr(:new,
> Base.Generator{Array{Float64,1},##1#2{Base.#sin}}, SSAValue(0), :(a)))
> return $(Expr(:invoke, LambdaInfo for
> Dict{K,V}(::Base.Generator{Array{Float64,1},##1#2{Base.#sin}}),
> :(Main.Dict), SSAValue(1)))
> end::Union{Dict{Any,Any},Dict{Float64,Float64},Dict{Union{},Union{}}}
>
> I have the folowing questions:
>
> 1. Why when f2 is used as written above the return type is not
> Dict{Float64,Float64} (like in the case of f1 where it is
> Array{Float64,1})?
> 2. How to fix f2 so that Julia can infer the return type?
> 3. Is there a way to change f2 so that first empty Dict{<element type
> of a>,<element type of t(a)>}() variable is created, where <element
> type of a> and <element type of t(a)> are determined based on the
> passed arguments, and only next this dictionary is populated with data?
>
> With kind regards,
> Bogumil Kaminski
>
