# Making \`broadcast\` compile-time inference more accurate
**URL:** https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345
**Category:** General Usage
**Tags:** question
**Created:** [June 19, 2017, 11:15am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345 "2017-06-19T11:15:20Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Dan](https://discourse.julialang.org/u/Dan)
#### Post date: [June 19, 2017, 11:15am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345/1 "2017-06-19T11:15:20Z")
Working on latest Julia, the following call is correctly inferred to be `Vector{Int64}`:
```julia
ww = [(1,2,3),(4,5,6)]
# this broadcast returns Vector{Int64}
broadcast(getindex,ww,1)
```
But,
```julia
qq = [(1,'a',1.0),(2,'b',2.0)]
broadcast(getindex,qq,1)
```
is only inferred weakly to be `Vector{Union{Int,Char,Float64}}`.
This is annoying, since `broadcast(first,qq)` is inferred better.
What should I define to help type-inference? Making `broadcast(getindex,qq,Val{1})` accurately inferred is also sufficient (as without knowing the value 1 at compile-time there is actually no way to know which tuple element is chosen).
This can be useful in cases where a record is parsed into a multi-typed tuple.
---
### Author:  [@tamasgal](https://discourse.julialang.org/u/tamasgal)
#### Post date: [June 19, 2017, 11:32am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345/2 "2017-06-19T11:32:07Z")
Hmm, I tried to reproduce it but failed:
```julia
v0.7.0-DEV.526> qq = [(1,'a',1.0),(2,'b',2.0)]
2-element Array{Tuple{Int64,Char,Float64},1}:
(1, 'a', 1.0)
(2, 'b', 2.0)
v0.7.0-DEV.526> broadcast(getindex,qq,1) |> typeof
Array{Int64,1}
```
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [June 19, 2017, 11:35am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345/3 "2017-06-19T11:35:00Z")
> [@Dan](#):
>
> Working on latest Julia
Do you mean 0.5.2? `broadcast` is much improved in Julia 0.6.
---
### Author:  [@Dan](https://discourse.julialang.org/u/Dan)
#### Post date: [June 19, 2017, 11:43am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345/4 "2017-06-19T11:43:45Z")
latest Julia today means: Version 0.7.0-DEV.635.
but the problem is not with the return type, but with the _inferred_ return type i.e.
```julia
@code_warntype broadcast(getindex,qq,1)
```
is `Vector{Union{Int64,Char,Float64}}` but `broadcast(first,qq)` has `Vector{Int64}` in `@code_warntype` and I want `broadcast(getindex,qq,Val{1})` to do the same.
---
### Author:  [@tim.holy](https://discourse.julialang.org/u/tim.holy)
#### Post date: [June 20, 2017, 3:12am UTC](https://discourse.julialang.org/t/making-broadcast-compile-time-inference-more-accurate/4345/5 "2017-06-20T03:12:43Z")
Woof, that’s a hard one. You’re passing a value (`1`) rather than a type, and hoping that the type system will constant-propagate it. You might have more luck defining `mygetindex` to take a `Val{1}`. But beware that `Val` objects are full of traps for the unwary, see [https://docs.julialang.org/en/latest/manual/performance-tips/#The-dangers-of-abusing-multiple-dispatch-(aka,-more-on-types-with-values-as-parameters)-1](https://docs.julialang.org/en/latest/manual/performance-tips/#The-dangers-of-abusing-multiple-dispatch-(aka,-more-on-types-with-values-as-parameters)-1) and the section immediately above it.