# Passing String parameters

**URL:** <https://discourse.julialang.org/t/passing-string-parameters/60211>\
**Category:** General Usage\
**Created:** [April 29, 2021, 1:12am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211 "2021-04-29T01:12:05Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![jrhut](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jrhut/32/24258_2.png) [@jrhut](https://discourse.julialang.org/u/jrhut)\
**Post date:** [April 29, 2021, 1:12am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/1 "2021-04-29T01:12:06Z")

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Hi there, I’m trying to pass a String to my function

foo (s::A, n::N=2) where {A\<:Union{String,Vector{String}}, N \<: Number}

I’m calling the function as so foo(“test”) and am receiving the error

MethodError: Cannot `convert` an object of type Char to an object of type String

I’m a little lost on how I am using a Char here? Any help would be great, cheers Jamie

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**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [April 29, 2021, 1:31am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/2 "2021-04-29T01:31:40Z")

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You are not using it in the function signature, that is for sure. That should work:

```julia
julia> foo(s::A, n::N=2) where {A<:Union{String,Vector{String}}, N <: Number} = s
foo (generic function with 2 methods)

julia> foo("test")
"test"

```

Thus, the problem is somewhere else. It is better if you post a snippet of code in which the error can be reproduced (in a fresh Julia section).

ps. Use the `</>` icon to write code within backticks, it becomes properly formatted.

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**Author:** ![jrhut](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jrhut/32/24258_2.png) [@jrhut](https://discourse.julialang.org/u/jrhut)\
**Post date:** [April 29, 2021, 1:37am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/4 "2021-04-29T01:37:44Z")

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Thanks for the response. Hmm I have pasted the code below but after some more tests I have found that if I run function from in the file it works as intended. It is only once the module is imported that the error begins. Not sure how this would effect my parameters though.

```julia
module Longurl
export expand_urls

using HTTP

"""
    Urls(expanded_url, status_code)
"""
struct Urls
    expanded_url::Vector{Union{String, Nothing}}
    status_code::Vector{Union{String, Nothing}}
end

"""
Takes a list of short urls and expands them into their long form

...
# Arguments
- `urls_to_expand::Array`: the list of short urls
- `seconds::Int64`: the timeout in seconds
# Returns
- `Urls`: Struct containing properties expanded_url and status_code
...
"""
function expand_urls(urls_to_expand::A, seconds::N=2) where {A<:Union{String,Vector{String}}, N <: Number} 

    if urls_to_expand isa String
        urls_to_expand = [urls_to_expand]
    end
    
    original_stdout = stdout
    original_error = stderr

    short_urls = Vector{Union{String, Nothing}}(nothing, length(urls_to_expand))
    expanded_urls = Vector{Union{String, Nothing}}(nothing, length(urls_to_expand))
    status_codes = Vector{Union{String, Nothing}}(nothing, length(urls_to_expand))

    i = 0
    for url in urls_to_expand
        i += 1
        last_head = nothing
        last_host = nothing
        last_code = nothing
        (rd, wr) = redirect_stdout()

        try
            HTTP.head(url, readtimeout=seconds, verbose=2, retry=false)
        catch e
            print(e)
        finally
            redirect_stdout(original_stdout)
            close(wr)  
            for line in readlines(rd)
                if occursin("HEAD", line)
                    last_head = split(line, " ")[2]
                end
                if occursin("Host", line)
                    last_host = split(line, " ")[2]
                end
                if occursin("HTTP/1.1 ", line)
                    last_code = split(line, " ")[2]
                end
            end
            short_urls[i] = url
            status_codes[i] = last_code
            expanded_urls[i] = last_host * last_head
        end
    end 
    
    long_urls = Urls(expanded_urls, status_codes)

    return long_urls

end

end

```

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<div class="post-metadata">

**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [April 29, 2021, 1:59am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/5 "2021-04-29T01:59:11Z")

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I could not reproduce the error you report here. If you provided a minimal (non-)working example, it will be easier to help.

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<div class="post-metadata">

**Author:** ![jrhut](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jrhut/32/24258_2.png) [@jrhut](https://discourse.julialang.org/u/jrhut)\
**Post date:** [April 29, 2021, 2:41am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/6 "2021-04-29T02:41:08Z")

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I have the module on github which includes the code I posted above.

> **[GitHub - jrhut/Longurl.jl: A Julia implementation of the R package longurl....](https://github.com/jrhut/Longurl.jl)**
>
> A Julia implementation of the R package longurl. For transforming short url's back into their long form. - GitHub - jrhut/Longurl.jl: A Julia implementation of the R package longurl. For tran...

I have attached an image that shows the error I am getting when importing this module. Cheers again I really appreciate this.

 ![image](https://global.discourse-cdn.com/julialang/original/3X/a/8/a89a60c3268e69e3a6cbb742227e1ccb1e4548c6.png)

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<div class="post-metadata">

**Author:** ![timbp](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@timbp](https://discourse.julialang.org/u/timbp)\
**Post date:** [April 29, 2021, 3:07am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/7 "2021-04-29T03:07:05Z")

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If you are getting Char, I suspect you are iterating through a String.

perhaps you want

```julia
expand_urls(["http://www.google.com"])

```

to iterate through an array

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<div class="post-metadata">

**Author:** ![jrhut](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jrhut/32/24258_2.png) [@jrhut](https://discourse.julialang.org/u/jrhut)\
**Post date:** [April 29, 2021, 5:13am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/8 "2021-04-29T05:13:31Z")

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Aha that makes sense! However I have now added a check to make sure if it is in fact a string it gets converted to a vector containing said string but I still seem to be getting the problem.

EDIT: I have figured out this problem is more down to my misunderstanding of the Julia package system. Thanks for all the help, it seems that whenever I called Pkg.add and using it was using an old version of the package even if I activated the environment with the new package. I went through and removed the old package files from my .julia and re added them and the issue was gone.

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<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [April 29, 2021, 5:29am UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/9 "2021-04-29T05:29:03Z")

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> [@jrhut](#):
>
> `expanded_url::Vector{Union{String, Nothing}}`

This sort of design isn’t normally ideal. I wouldn’t write the function to accept both strings _and_ vectors of strings. It’s cleaner and less error prone to write your function to accept strings, and then iterate _outside_ your `expand_urls` function (and call it `expand_url`), using for example broadcasting.

And then consider defining your `Urls` struct to only accept scalars and create a vector of `Url`s, instead of holding the vectors _inside_ a single object.

I think this would be a lot cleaner.

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<div class="post-metadata">

**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [April 29, 2021, 12:18pm UTC](https://discourse.julialang.org/t/passing-string-parameters/60211/10 "2021-04-29T12:18:19Z")

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> [@jrhut](#):
>
> I have figured out this problem is more down to my misunderstanding of the Julia package system.

I think the easiest way to avoid that kind of problem is to go to the directory of the package and start Julia with

```julia
julia --project

```