How to make String with Placeholders?

DimWell

Hi Experts,

I am looking for built in function something like String builder with Placeholders.
Iet say in C like languages usuall you wold have function that looks like:

print(" Some string %placeholder1, string continues…%placeholder2 ", var1, var2)
#vars goes to placeholders

`Do we have something similar in Elixir ?

Use Case:
User provides: custom url with placeholders and separately details.
Then later url should be combined with data into proper url.

User: 223344
Lang: eng
Type: json | xml

Original URL

http: // somesite. com/?i=#{id}&lang=#{language}&type=api&api_v=1&api_type=#{data_type}"

Updated URL

https: // somesite. com/?i=#223344&lang=#eng&type=api&api_v=1&api_type=#json"

15 comments

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2021-12-24 02:38:38 UTC

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trollfred

It is a bit awkward, that there is no nicer way

Post #15

mguimas

I suggest you to use :io_lib.format(format, [arg1, ...]) |> to_string(). See the documentation of :io_lib.format.

It is one less dependency if you use this function because it is in the standard library.

Post #14

hassan

Are you using Phoenix by any chance? If so take a look at:

Routing — Phoenix v1.8.8

Might give you some ideas regardless…

Post #13

michalmuskala

Format is rather experimental right now and has some issues especially around formatting floats. Maybe I should finally get into it an finish it, now that Jason is mostly done

Post #12

DimWell

Hi jfeng,

Thank you for advice :+1 , but I probably had to mentioned that I would prefer not to add extra dependencies. Meanwhile, I can have a look, into their code and analyse it to get more ideas.

Post #11

DimWell

Hi jakemorrison,

Thank you for a good point. You are absolutely right.

Post #10

jfeng

One way is with Michał Muskała’s Format library GitHub - michalmuskala/format: A simple string formatter for Elixir · GitHub. I’m not sure if there’s any documentation, but you can do:

def print_url(id, language, url) do
  url
  |> Format.compile()
  |> Format.string(id: id, language: language)
  |> IO.puts()
end

where url is a string that contains {id} and {language}, which get replaced by the corresponding values specified in Format.string.

My personal syntactic preference would be

...
  |> Format.string([id: id, language: language])
...

Post #9

jakemorrison

You should generally be using the URI module to deal with URLs: URI — Elixir v1.20.2
That will handle the escaping, otherwise you will have plenty of surprises with strange data.

Post #8

DimWell

Thank you guys for help !

Post #7

DimWell

Yep…
Well, I know that I can parse url…

The point is that this solution is not flexible…
This would work good on static urls, that do not change…

In cases where url can be any, probably it is better to use cpgo’s solution.
In my case I cant know in advance all possible urls, but I can tell user use the fallowing layout… and the test if user provides url according to layout and if it is matches then execute as a template…

Post #6

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