Overload Phoenix.HTML.Safe for list of floats

Phoenix Forum Questions / Help
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1

Phoenix won’t directly print a list of floats on a page

there is already a Phoenix.HTML.Safe protocol for lists but the list of floats are excluded

is it possible to overload only that specific part of the protocol to add a special formatting for a list of floats (representing some coordinates) ?

or is it mandatory to build a new ecto type ?

2

You could create a small view function that takes a list of floats and turns them into a string and call that from your template. You will then get control over how they are displayed (e.g. decimal places).

This is the general pattern - things like maps and tuples also need specific rendering helper functions in your views.

2 Likes
3

Helpers methods in your views is the way to go as by previous response.

I needed same for my charting and I was lazy so I just called Jason.encode(floatlist)

4

yes but I get the array of float from a text input in a form and I would like the changeset to reflect the correct value without tweaking when the form comes back

for a field f1 which is {:array, :float}
I use 45 / 56 in the form to get [45.0, 56.0] after ad hoc parsing but then the value does not print back in the form because array of floats…
<%= text_input f, :f1 %> fails
I would need to add value: small_function(f.data.f1) but I would like it to be automatic through specific type maybe

5

Well your issue is not printing floats. It is your form structure.

Your should have in your form

for value <- myArray
number_input numbers ... name: myArray[] value: value
end

You will receive an array of strings in your myArray

Your changeset should cast them to float for you.

6

I did that before, but I want only one text field for the components of the array and parse them from a string,
for more compactness in the user interface

once the changeset get the parsed floats values it cannot print back in the form unless maybe using some ecto type, or a specific protocol , or manually tweaking with value: some_formatting(data)

7

yes in your use case the available option is that and you will have the cater for parsing incoming value as an array too.

8

so there is no other option ?
not possible to add a Phoenix.HTML.Safe impl for this specific case ?

with a specific ecto type I can get automatic parsing on read with the cast callback from the text input field, but I cannot print it back in the form field without ad hoc formatting

9

You absolutely could but seems like an overkill. If you have the need go for it.

AFAIK you can not, HTML forms can do so much