# Auto conversion for type constructor doesn't work for parameter types

**URL:** <https://discourse.julialang.org/t/auto-conversion-for-type-constructor-doesnt-work-for-parameter-types/1566>\
**Category:** General Usage\
**Tags:** question\
**Created:** [January 18, 2017, 11:13am UTC](https://discourse.julialang.org/t/auto-conversion-for-type-constructor-doesnt-work-for-parameter-types/1566 "2017-01-18T11:13:25Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![FANG\_Colin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fang_colin/32/170_2.png) [@FANG\_Colin](https://discourse.julialang.org/u/FANG_Colin)\
**Post date:** [January 18, 2017, 11:13am UTC](https://discourse.julialang.org/t/auto-conversion-for-type-constructor-doesnt-work-for-parameter-types/1566/1 "2017-01-18T11:13:25Z")

</div>

Does auto conversion for type constructor not work for parameter types on purpose?

```julia
immutable A
    x::Float64
    y::Int
end
A(1, 2) # Works

immutable B{T}
    x::Float64
    y::Vector{T}
end
B(1, [2]) # Error

```

---

<div class="post-metadata">

**Author:** ![mauro3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mauro3/32/292_2.png) [@mauro3](https://discourse.julialang.org/u/mauro3)\
**Post date:** [January 18, 2017, 11:25am UTC](https://discourse.julialang.org/t/auto-conversion-for-type-constructor-doesnt-work-for-parameter-types/1566/2 "2017-01-18T11:25:26Z")

</div>

Note that this works:

```julia
julia> B{Int}(1, [2])
B{Int64}(1.0,[2])

```

This outer constructor is missing:

```julia
julia> B{T}(x,y::Vector{T}) = B{T}(x,y)
B

julia> B(1, [2])
B{Int64}(1.0,[2])

```

Related [Constructor with partially specified type parameters fails to fallback to convert method · Issue #18203 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/18203), [https://github.com/JuliaLang/julia/issues/17186](https://github.com/JuliaLang/julia/issues/17186)