Default values for variables

[vascop]

Is there a way to use a default value when a variable isn't defined?

Something like:
{{(ds "config").notes | default "this a default note")}}

[hairyhenderson]

@vascop Not in a general sense right now. For your specific example, that might result in an error if the config datasource doesn't have a notes key. I'd have to dig a little further into it to make sure.

Either way - this is a good idea! Thanks for logging this issue 🙂

[zealic]

I think we need a new func: hasKey

like hugo's isset

{{ $config := (ds "config") -}}
{{ $notes := "this a default note" -}}
{{ if hasKey $confg "notes" -}}
{{ $notes := $config.notes -}}
{{ end -}}

[hairyhenderson]

@zealic there is has/conv.Has already: https://gomplate.hairyhenderson.ca/functions/conv/#conv-has

[hairyhenderson]

And actually, that's an excellent point... @vascop will has fix your use case? What @zealic suggested should work (except use has instead of hasKey).

[vascop]

I think it'd probably work, though much more verbose since we'd have to do the whole "check if it has key and overwrite" dance instead of one-lining the default values.

[hairyhenderson]

@vascop understood. It's not ideal. But it might be the only option...

The challenge is that referencing an undefined key will cause Go's text/template to blow up:

$gomplate -i '{{ (json `{"foo":"bar"}`).baz }}'
panic: template: template:1:9: executing "template" at <`{"foo":"bar"}`>: map has no entry for key "baz"

goroutine 1 [running]:
main.(*Gomplate).RunTemplate(0xc42030e030, 0x7fff5fbff54c, 0x20, 0x1e95de0, 0xc42000c018)
	/go/src/github.com/hairyhenderson/gomplate/gomplate.go:31 +0x42c

My impression is that we won't be able to get that specific syntax to work without re-implementing Go's templating system.

What we can do is have a default function that will provide a value if the given input is nil or an empty string. That's not too difficult, but it wouldn't address your specific use-case.

[estahn]

👍 for default, e.g. {{ .foo | default "bar" }}.

[hairyhenderson]

@estahn if . has no foo key, that particular usage will never work. In that case you'll have to always wrap it in {{ if has . "foo" }}...{{ end }}.

But I still think default would be useful for handling empty values. I'll see about implementing this soon.

[thepalbi]

Just for future reference, I'm using this to make something like that default case:

{{ has (ds "config") KEY | ternary (ds "config").KEY "default value" }}

[studioph]

Wanted to share another option that I found works and is pretty close to the sprig version as well. I'm configuring my datasources as contexts in the config file in this case.

{{ index . "foo" | default .values.defaults.foo }}