Question: How can I do a different action if it is the last iteration of a loop

[loque1]

This is less of an issue but more of a question
I have some yaml :

port_mappings:
   - test1:
      container_port: 8080
      protocol: "tcp"
      app_protocol: "http2"
   - test2:
      container_port: 9090
      protocol: "udp"
      app_protocol: "http"

This is passed into a template :

{{ if has .config "port_mappings" }}
      "portMappings": [
      {{ range $key, $port_map := .config.port_mappings  }}
        {{ range $key, $value := $port_map  }}
        {
          "containerPort": {{ if has $value "container_port" }}{{ $value.container_port }}{{ else }}80{{end}},
          "protocol": "{{ if has $value "protocol" }}{{ $value.protocol }}{{ else }}tcp{{end}}",
          "appProtocol": "{{ if has $value "app_protocol" }}{{ $value.app_protocol }}{{ else }}http{{end}}"
        },
        {{ end }}
      {{ end }}
      ],
      {{ end }}

I want the last iteration not to add the "," so the rendered template is a valid json array like :

"portMappings": [
        {
          "containerPort": 8080,
          "protocol": "tcp",
          "appProtocol": "http2"
        },
        {
          "containerPort": 9090,
          "protocol": "udp",
          "appProtocol": "http"
        }
      ],

In other templating options there is built in $last signal that one can use. I can not find this type of option on how to do this.
Is there a way I can construct this type of approach ?

Thanks for the all the incredible work on the tool.

[hairyhenderson]

This is less of an issue but more of a question [...]

@loque1 in that case, I've converted the issue to a discussion 😉

When ranging through .config.port_mappings, because it's an array, $key is actually the index. You might be able to use the len builtin to find out if you're on the last element... Something like:

{{ if ne (sub (len .config.port_mappings) 1) $index }},{{end}}

(this is kind of like if index != len(port_mappings) - 1 { printf(",") })

That solves the comma after the [], but for the map it's a bit more complex - one property of Go templates (and hence, gomplate) that's different from Go is that map keys are ordered naturally during iteration:

If the value is a map and the keys are of basic type with a defined order, the elements will be visited in sorted key order.

So, a kind of hacky way to detect whether you're on the last element could be to iterate through the map twice, setting a $lastKey variable the first time, then comparing against it the second:

{{ $lastKey := "" }}
{{ range $key, $value := myMap }}{{ $lastKey = $key }}{{ end }}
{{ range $key, $value := myMap }}
...
  {{ if ne $lastKey $key }},{{ end }}
{{ end }}

Hope that makes sense!

I'll bet there are simpler ways to approach this, however 😉

[loque1]

Cheers and thanks for the speedy response. I was hoping there was a built in that could work this out that I could reference like a {{ last}} or {{ first }} type operator that would do the heavy lifting. Once again thanks for the answer and keep up the great work